Regeneration in video games refers to the gradual recovery of health, absent other healing items or abilities.
Until Battlefield 1943, a player's health could only be restored by medkits (or by defibrillator if killed). Other healing items such as Medkits, Bandages, Auto Injectors (depending on the game) are required to regain health. Some of these healing items may induce a regeneration over time effect, but they are not true regeneration in a gameplay mechanic sense because they still need to be activated with an item.
Health regeneration is typically faster in singleplayer than in multiplayer.
Battlefield 1943 is the first game in the Battlefield series that introduces health regeneration. Though, the game lacked a health meter, the screen was used instead. Whenever a player took more and more damage, the screen got more red crawling around the edges. When it reached the middle, the player gets killed.
Battlefield: Bad Company 2
Battlefield: Bad Company 2 features health regeneration in both singleplayer and multiplayer. In multiplayer, it does not work nearly as fast as a medkit, but allows an isolated soldier to recover.
Battlefield 3 features health regeneration of both players and vehicles. Players regenerate health after a period of time. Attacks by enemies, including suppressive fire, halt regeneration. Again, medic kits heal at a faster rate than regeneration alone. Medic kits can regenerate health even when the player is suppressed.
Regeneration begins 16 seconds after taking damage, at a rate of 5 hp/sec. If the player exits the range of a medic kit without full health, the regeneration begins after 12 seconds.
Any vehicle that has not caught fire or been disabled can also recover health. The Maintenance specialization increases the regenerative effect, though still not as fast as can be repaired by an Engineer's Repair Tool.
Server administrators can disable regeneration in Custom game settings.
Health regeneration is still present in Battlefield 4 for both players and vehicles, functioning in a similar manner to Battlefield 3.