A man cave, sometimes a mantuary or manspace, is a male sanctuary, such as a specially equipped garage, spare bedroom, media room, den, or basement. It is not a cave but rather a metaphor describing a room inside the house, such as the basement or garage or attic or office, or outside the house such as a wood shed or tool room, where "guys can do as they please" without fear of upsetting any female sensibility about house decor or design. Paula Aymer of Tufts University calls it the "last bastion of masculinity".

While a wife may have substantial authority over a whole house in terms of design and decoration, she generally has no say about what gets "mounted on the walls" of a man's personal space. Since it may be accepted that a woman has input on the decoration of the rest of the house, a man cave or man space is in some sense a reaction to feminine domestic power.

Man caves have multiple purposes: they're a place to be alone, to be away from women and from female sensibilities, to indulge in hobbies, and to hang out with male friends. It is, loosely, a male-only space to retreat to, Man Caves, watch sports matches, or play video games. According to psychiatrist and author Scott Haltzman, it is important for a man to have a place to call his own, referring to a male area to which to retreat. Some psychologists claim that a man cave can provide refuge from stressful surroundings and be beneficial to marriage. Rules are relaxed; it is a place where other people's sensibilities about standards of cleanliness are not necessarily observed; as one man said, "You spill a beer there or leave a hamburger overnight, who cares?"

In English, lower case man (pl. men) refers to an adult human male (the term boy is the usual term for a human male child or adolescent). Sometimes it is also used as an adjective to identify a set of male humans, regardless of age, as in phrases such as "men's rights". Although men typically have a male reproductive system, some intersex people with ambiguous genitals, and biologically female transgender people, may also be classified or self-identify as a "man".

The term manhood is used to refer to masculinity, the various qualities and characteristics attributed to men such as strength and male sexuality.

The English term "man" is derived from Old English mann. The Old English form had a default meaning of "adult male" (which was the exclusive meaning of "wer"), though it could signify a person of unspecified gender. The closely related "man" was used just as it is in Modern German to designate "one" (e.g., as in the saying Man muss mit den Wölfen heulen). The Old English form is derived from Proto-Germanic *mannaz, "persona", which is also the etonym of German Mann "man, husband" and man "one" (pronoun), Old Norse maðr, and Gothic manna. According to Tacitus, the mythological progenitor of the Germanic tribes was called Mannus. The Germanic form is in turn derived from the Proto-Indo-European root *manu-s "man, person", which is also the root of the Indian name Manu, mythological progenitor of the Hindus.

A cave or cavern is a natural underground space large enough for a human to enter. The term applies to natural cavities some part of which is in total darkness. The word cave also refers to smaller spaces like rock shelters, sea caves, and grottos.

Speleology is the science of exploration and study of all aspects of caves and the environment which surrounds the caves. Exploring a cave for recreation or science may be called caving, potholing, or, in Canada and the United States, spelunking (see caving).

The formation and development of caves is known as speleogenesis. Caves are formed by various geologic processes. These may involve a combination of chemical processes, erosion from water, tectonic forces, microorganisms, pressure, atmospheric influences, and even digging.

Most caves are formed in limestone by dissolution.

Solutional caves are the most frequently occurring caves and such caves form in rock that is soluble, such as limestone, but can also form in other rocks, including chalk, dolomite, marble, salt, and gypsum. Rock is dissolved by natural acid in groundwater that seeps through bedding-planes, faults, joints and so on. Over geological epochs cracks expand to become caves or cave systems.