A tactical shooter is a subgenre of shooter game that includes both first-person shooters and third-person shooters. These games typically simulate realistic combat, thus making tactics and caution more important than quick reflexes in other action games. Tactical shooters involving military combat are sometimes known as „soldier sims“.
Tactical shooter is a shooter that generally simulates realistic, squad-based or man-to-man skirmishes. Notable examples of the genre include Ubisoft’s Tom Clancy’s Rainbow Six and Ghost Recon series and Bohemia Software’s Operation Flashpoint.

Game design
Tactical shooters are designed for realism. It is not unusual for players to be killed with a single bullet, and thus players must be more cautious than in other shooter games. The emphasis is on realistic modeling of weapons, and power-ups are often more limited than in other action games. This restrains the individual heroism seen in other shooter games, and thus tactics become more important. Overall, the style of play is typically slower than other action games. Jumping techniques are sometimes de-emphasized in order to promote realism, with some games going so far as to omit a jump button. In contrast to games that emphasize running and shooting, tactical shooters require more caution and patience, and games are sometimes designed so that shooting becomes inaccurate while running. Some tactical shooters lack the crosshair seen in other first-person shooters, in order to achieve a high degree of realism.
Many tactical shooters make use of group-based combat, where the player character is supported by other teammates. While early tactical shooters had simple computer-controlled teammates who offered support fire, the artificial intelligence in later games has evolved with more complex teammate responses such as cover-fire mechanics. In games with a sufficiently robust artificial intelligence, the player character is able to issue commands to other computer-controlled characters. Some games in the genre allow players to plan their team’s movements before a mission, which the artificial intelligence then follows. Many games also offer a multiplayer online play, allowing human players to strategize. Team-based tactics are emphasized more than other shooter games, and thus accurate aiming and quick reflexes are not always sufficient for victory.
The level design usually reflects the game’s setting. For example, the player may play the role of police fighting terrorists or other criminals, or may engage in military combat in real world conflicts. Some games even take place in entirely fictional universes, and incorporate elements of science fiction. Each level will have different objectives. Although some levels may simply require the player defeat their enemy, other levels may challenge the player to escort a VIP safely to a specific location. Levels are often designed with choke points or alternate routes. It becomes important to exploit a superior position, or take the enemy by surprise.

Origins
The tactical shooter genre was pioneered in 1998. One key title was Delta Force, which emphasized real-world weaponry and quick kills.The genre was also influenced by the SWAT series, a spin-off from the Police Quest series of adventure games. But the game industry generally credits games such as Rainbow Six and Counter-Strike with defining and refining the tactical shooter genre. Counter-Strike maintained its status as one of the best games in the genre, even years after its release.
Rainbow Six has been credited as a revolutionary game, which defined the conventions of the genre. The game was inspired by the Federal Bureau of Investigation Hostage Rescue Team, and was designed to replicate a team of specialists performing a skilled operation. The game was designed to emphasize strategy in a way that would be fun for players without the best reflexes.The series has since become a benchmark for the genre in terms of detail and accuracy.

Sources: Wikipedia Modified by Fanterazzi