An atoll ( /ˈætɒl/ or /æˈtɒl/) is a coral island (or islands) that encircles a lagoon partially or completely.

The word atoll comes from the Dhivehi (an Indo-Aryan language spoken on the Maldive Islands) word atholhu (Dhivehi: އަތޮޅު, [ˈət̪ɔɭu])^OED. Its first recorded use in English was in 1625 as atollon - Charles Darwin recognized its indigenous origin and coined, in his The Structure and Distribution of Coral Reefs, the definition of atolls as "..circular groups of coral islets [...] and [the word] is synonymous with 'lagoon-island'." (1842, p. 2). More modern definitions of atoll are those of McNeil (1954, p. 396) as "..an annular reef enclosing a lagoon in which there are no promontories other than reefs and islets composed of reef detritus" and Fairbridge (1950, p. 341) "...in an exclusively morphological sense, [as] ...a ring-shaped ribbon reef enclosing a lagoon."

The distribution of atolls around the globe is instructive: most of the world's atolls are in the Pacific Ocean (with concentrations in the Tuamotu Islands, Caroline Islands, Marshall Islands, Coral Sea Islands, and the island groups of Kiribati, Tuvalu and Tokelau) and Indian Ocean (the Atolls of the Maldives, the Laccadive Islands, the Chagos Archipelago and the Outer Islands of the Seychelles). The Atlantic Ocean has no large groups of atolls, other than eight atolls east of Nicaragua that belong to the Colombian department of San Andres and Providencia in the Caribbean Sea.

Robert Kelly Slater (born February 11, 1972, Cocoa Beach, FL, USA) is an American professional surfer known for his competitive prowess and style. He has been crowned ASP World Champion a record 11 times, including 5 consecutive titles from 1994–98. He is the youngest (at age 20) and the oldest (at age 39) to win the title. Upon winning his 5th world title in 1997, Slater passed Australian surfing legend Mark Richards to become the most successful champion in the history of the sport. In 2007 he also became the all-time leader in career event wins by winning the Boost Mobile Pro event at Lower Trestles near San Clemente, California. The previous record was held by Slater's childhood hero, 3-time world champion Tom Curren.

In addition to the ASP tour, Slater has also competed in the X-Games (in 2003 and 2004). After earlier being awarded the title prematurely as a result of a miscalculation by the ASP, on November 6, 2011 Slater officially won his eleventh ASP world title at the Rip Curl Pro Search San Francisco, by winning his 4th round heat. In May 2005, in the final heat of the Billabong Tahiti Pro contest at Teahupo'o, Slater became the first surfer ever to be awarded two perfect scores for a total 20 out of 20 points under the ASP two-wave scoring system. (The corresponding honor under the previous three-wave system belongs to fellow American Shane Beschen who achieved the feat in 1996.) Since 1990, Slater has been sponsored primarily by surfwear industry giant Quiksilver. He exclusively rides Channel Islands surfboards equipped with his own signature series of FCS fins.