This is a guide to some of the technical or obscure terms related to the hobby of infiltration. We don't use code language or jargon to exclude anyone, but because it's a specialized hobby we've had to adopt or invent some specialized terms. Thanks to FiL for much of the draining vocabulary. If you think an oft-used term is missing, please let me know.

abseil <German> v. rappel; see rappel
back breaker adj. long, low tunnel in a drain
ball buster adj. round concrete pipe drain with wide section of water
BASE jump v. leap from buildings, antennae, spans (bridges and trams) or earth (cliffs); not really infiltrating, but some infiltrators feel solidarity with base jumpers
buildering n.,v. climbing buildings, with or without tools and support devices
bunker n. underground military command post, as found throughout Australia and Europe, particularly in Britain
burn v. ruin for others through lack of subtlety (i.e. "some guys burned the new tunnels by tagging everywhere, now they're kept locked")
cacophony society n. a group whose members pursue "experiences beyond the pale of mainstream society through subversion, pranks, art, fringe explorations and meaningless madness" and who share some ideals with urban explorers
carriere <French> n. a manmade cave, leftover from mining operations
catacomb n. subterranean burial grounds and the mazes of tunnels connected to them, as found in several older European cities, including Paris and Rome (strictly speaking, the term "catacomb" only applies to the burial grounds)
cataphiles n. those who explore catacombs
catch basin n. tank located under the street where water collects before flowing into drains
central utilities building or CUB n. on a college or university campus, the building that supplies the rest of the campus with electricity, heat, cool air and water, usually via steam tunnels
chamber n. huge, long room in a drain
chatière <French> n. squeeze hole (literally "cat hole") used to enter or exit tunnels
chimneying v. climbing by using various body parts to provide force on opposing walls
chud <from C.H.U.D., 1984 horror movie> n. you don't want to know what it means (but if you did, I'd tell you it meant cannibalistic humanoid underground dweller)
CIHY n., v. short for "can I help you?"; query often directed at infiltrators
Clannies n. annual award night/party held by explorers in Melbourne and Sydney at the conclusion of the Australian draining season
closed circuit television or CCTV n. television signals transported directly from a camera to a monitor via wires, without broadcasting
college tunnel n. see steam tunnel
combined sewage overflow or CSO n. in older drainage systems, storm sewers and sanitary sewers may be connected to some degree, resulting in this unfortunate occurrence during serious storms
crater <climbing jargon> v. to fall from a height and hit the ground (as in, "I almost cratered!")
credibility prop n. an item such as a clipboard or briefcase, carried or used by an infiltrator to reduce suspicion
creeper n. one who infiltrates
cut-and-cover adj. subway tunnels created by a process of digging down from the top and covering up the hole, as opposed to boring a tube
darkie n. see stormwater drain
digestive <from Senor Jojo> adj. a full-length expedition that goes in one end and out the other
diggers n. group of underground explorers in Russia
draining v. exploring stormwater drains (see stormwater drain)
drop n. a small waterfall in a drain
elevator surfing v. the dangerous activity of riding on top of a moving elevator
expo <from expedition> n. a mission attempted by a group of people
flashlight n. American/Canadian word for torch
freighthopping v. stowing away aboard freight trains in order to get free transport; not really infiltrating, but some infiltrators feel solidarity with freighthoppers
geocaching v. using GPS units to locate hidden caches of goods based on co-ordinates and clues; not really infiltrating, but some infiltrators feel solidarity with geocachers
grilles n. metal bars found in the roof or sides of a drain; rooms made entirely of grilles are called grille rooms
gutter box n. small space or room underneath the slit in a gutter into which water falls before emptying into the drain itself
hacking <used at MIT> v. 1. synonym for infiltrating; sometimes known by the full name of roof and tunnel hacking 2. installing or being otherwise involved in the execution of a classy prank
HEPA filter n. high efficiency particulate air filters, useful in keeping asbestos fibres out of one's respiratory system
hoarding n. the temporary wooden walls surrounding a construction or demolition site
infiltration n.,v. going places you're not supposed to go in general; covers urban exploration as well as simply dropping in to conventions uninvited and the like
junction n. point where two sections of a drain meet; a junction room is a room where two tunnels join into one
labyrinth n. a series of connected tunnel systems built for different purposes
Lift-o-Matic n. simple manhole key produced by the Cave Clan
loop n. two distinct drain tunnels separating but rejoining further upstream or downstream
maglite n. favoured brand of flashlight/torch
manhole n. name for either a hole in the street leading underground or the underground room itself; sometimes used as shorthand for "manhole cover"
master key n. a key that opens all, or almost all, the doors in a particular institution
metro n. the name for the subway system in both Paris and Montreal
mice n. slang for campus security guards
mole people n. the hundreds or thousands of people who live in the tunnels under New York City, according to a book of dubious merit of the same name by Jennifer Toth
mousehouse n. slang for campus security office
mummy n. tunnel shape so named because it resembles a mummy's sarcophagus (referred to by the water board as a horseshoe)
outfall n. the spot where a storm drain empties its water out into nature; a popular entrance and exit point for explorers
overflow n. a drain separate from the main tunnel built to carry excess water when the water level in the main tunnel is high; normally dry
parkour n. French sport involving climbing up, jumping onto and falling off of manmade structures; often described as skateboarding without a skateboard
physical plant n. at a college or university campus, the department which is responsible for maintaining the central utilities building and the steam tunnels; sometimes also used as a synonym for central utilities building
popper n. device used to open a manhole cover; the Lift-o-Matic is one kind
rainslot n. see catchbasin
ramp n. in a drain, a slope not steep enough to be a slide
rappel v. descend a wall or steep face using a doubled rope
rebar n. steel reinforcing rod used in concrete
RCP n. round concrete pipe (usually used in reference to the drain shape)
RT adj.,n. rapid transit, sometimes used as a short form for "train that runs on a rapid transit system"
sanitary sewer n. a sewer that isn't sanitary — that is, the kind most drainers avoid
seccers n. short for security guards
sewering n.,v. exploring sanitary sewers (occasionally misused as a synonym for draining, see draining)
shaft n. vertical passage connected to a tunnel; v. to climb up or down a shaft without climbing tools
shrinker n. drain that just continues to get smaller as you head upstream
sign-in <used at MIT> n. a small personal mark in an area that one is proud of having found or climbed to, usually dated so future explorers can get an idea of when people have been there; not intended for anyone but other explorers to see
slide n. steep section of a drain, steeper than a ramp
skunneling <skateboarding and tunneling> n.,v. skateboarding in drains
social engineering <from hacker jargon> n.,v. dealing with people (employees, security guards) in a manner that allows you to get past them or obtain information from them
snotsicle <from Action Squad> n. small, mucus-like stalactite that hangs from the ceiling of certain moist sewers
spelunking <from caver jargon> n.,v. exploring caves, whether natural or manmade; most (natural) cavers prefer to think of themselves as speleogists rather than spelunkers
split n. part where a drain divides
steam tunnel n. underground passages that house pipes carrying steam and other utilities; found under large colleges, universities and other large institutions
step irons n. metal rungs set into a wall to provide a ladder
storm sewer n. see stormwater drain
stormwater drain n. underground tunnel that shuttles rain or melted snow from urban areas back out to the wilds of nature where it belongs
stunneling <student or steam tunneling> n.,v. travelling through steam tunnels under colleges or universities
tabi <Japanese> n. footwear with a split between the big toe and the rest of the foot; ideal for climbing
tag (up) v. write graffiti consisting of nothing more creative than an explorer's name
texta n. big, thick marker used for graffiti
third rail n. the electrified rail that powers most subway systems; to be avoided
tomb n. 1. synonym for drain used when the drain is named after someone, from a Melbourne tradition of members naming drains after themselves (i.e. Sloth's Tomb, Bob's Tomb) 2. <used at MIT> an unused space, usually with only one entrance, named by the discoverer
topside n. above ground
torch n. British/Australian word for flashlight
tract n. pamphlet circulated among cataphiles, often via the catacombs
trainhopping v. see freighthopping
tube n. subway tunnels created by a boring machine, or a nickname for the London Underground
uberboots <Albertan> n. rubber boots that come up to one's knees or higher
Underground, the n. 1. the oldest and one of the largest subway systems in the world, in London 2. popular urban exploration mailing list
urban adventure n. very much like urban exploration, but with the focus upon experiences rather than sight-seeing
urban exploration n. the investigation of manmade structures not designed for public consumption, from mechanical rooms to stormwater drains to rooftops; usually such areas are off-limits
vad <derived from the hacked command for the computer text game Adventure> v. explore - the word adopted by MIT students for real-world hacking
viewing hole n. an eye-level hole, usually rectangular, cut into the boards surrounding a construction site to appease curious passersby
water moccasin n. poisonous snake rumoured to inhabit drains in the southern USA
waterfall n. in a drain, a large drop over which the drain water falls
yabbies <from Australian> n. fresh water crustaceans found in Australian drains