Urban Terror, commonly abbreviated as UrT is a total conversion mod of id Software's first-person shooter Quake III Arena by Silicon Ice Development (hereafter referred to as Frozen Sand). It introduces many elements of the tactical shooter genre — team-driven gaming in more realistic environments.

Urban Terror is focused on blending realism with the fast-paced action of shooters such as Quake III Arena and Unreal Tournament. The realism in the mod is introduced through a number of changes. The weapons available are real-life, have recoil, are less accurate when fired while moving, and require reloading after a magazine has been expended. The number of weapons and other gear that can be carried is limited.

Damage is also realistic, based on dividing the player target into discrete areas. In addition to the damage system, wounds require bandaging, and wounds sustained in the legs or feet slow the player down considerably until they are bandaged. A stamina system is also present, and is depleted by activities such as sprinting or jumping; crouching down allows the stamina bar to recover faster. Depending on the map being played, external environments are more realistic too and can include weather effects such as rain or snow.

Urban Terror breaks from traditional realism games like Rainbow Six by allowing players to perform superhuman feats. Strafe jumping is a good example, and has been featured prominently in numerous jump movies produced by the community. Damage is another key example; while damage taken depends on the part of body which is hit, one can keep going after receiving numerous hits.

Further breaking from reality, Urban Terror includes walljumping, ledge climbing, and power sliding. Walljumping allows players to literally jump off walls, while ledge climbing allows players to grab onto certain ledges, and power sliding lets them move rapidly in a crouched position. Urban Terror also retains the movement speeds from Quake 3 Arena which - particularly in combination with strafe jumps - makes players move through the screen incredibly quickly.

Source: Wikipedia