Capture the Flag (CTF) is a traditional outdoor sport where two or more teams each have a flag (or other markers) and the objective is to capture the other team’s flag, located at the team’s “base” (or hidden or even buried somewhere in the territory), and bring it safely back to their own base. Enemy players can be “tagged” by players when out of their home territory and, depending on the rules, they may be out of the game, become members of the opposite team, be sent back to their own territory, be frozen in place, or be sent to “jail” until freed by a member of their own team.
Merriam-Webster Online Dictionary
capture the flag (noun) a game in which players on each of two teams seek to capture the other team's flag and return it to their side without being captured and imprisoned
