A reality hacker is an urban spelunker. "Building hacker" is a better term than "reality hacker" for participants in urban exploration activity. Using the definition of hacker that the mainstream media uses, a reality hacker is like a computer hacker but instead of hacking into computers, a reality hacker "hacks" (enters without authorization, trespasses, explores) in real life.

A reality hacker is an explorer of the underlying reality of existence; using any tools available. Science is an important subset of reality hacking. Classical mysticism is another. The hacking part means, as with other forms of hacking, learning of capabilities that the ordinary user may never realize are in the system. This uses the definition of hacker used by computer programmers, not the mainstream media.

Reality Hackers was an earlier name for Mondo 2000 magazine.

In the Mage: The Ascension role-playing game, the Reality Hackers are a sub-group of the Virtual Adepts.