1. Someone who makes a hobby of exploring caves, "a caver".
2. Another term for a speleologist.
3. Etymology: "A cave bug; one who explores caves as a hobby", 1942, formed from obsolete spelunk "cave, cavern" (c.1300), from Old French spelunque, from Latin spelunca, "a cave, cavern, grotto", from Greek spelynx (genitive spelyngos). An adjective, speluncar "of a cave" is recorded from 1855.

Also known as urban exploration (urbex or UE), is the examination of the normally unseen or off-limits parts of human civilization.

Urban spelunking is also commonly referred to as "infiltration", although some people consider infiltration to be more closely associated with the exploration of active or inhabited sites.

In the U.S.A., it may also be referred to as "draining" (when exploring drains) "urban exploration", and "urban caving."