The Inhibitors are buildings that block the training of enemy Super Minion in the same lane. Once an enemy team's inhibitor is destroyed, the Nexus will start spawning Super Minions in the corresponding lane on the next wave, along with giving a boost of roughly 100hp to all the regular minions in all 3 lanes for future waves. Regular minions spawned while the inhibitor is down receive additional attack damage. Ranged and melee minions in all lanes receive a bonus amount based on the number of enemy inhibitors destroyed as their wave spawns.
Each team has 3 Inhibitors on Summoner's Rift and 2 on Twisted Treeline, of which at least one must be destroyed for the Nexus and its turrets to be vulnerable to attack. Every inhibitor is protected by a turret; while this turret is up, the inhibitor is invulnerable to attacks. When all of the enemy team's inhibitors are destroyed, each lane spawns two Super Minions per minion wave.
Destroyed inhibitors respawn after a certain amount of time, resulting in Super Minions no longer being trained and the removal of normal minions' bonus health. The respawn time previously increased every time the inhibitor was destroyed, but since the V188.8.131.52, it is a consistent 5 minutes.
Once its protecting turret is destroyed the inhibitor is extremely susceptible to backdooring. An enemy carry will be able to take down an unprotected inhibitor before a defending champion can recall and walk to defend it. Additionally, one can't directly Teleport to it. Destroying an inhibitor can often be worth more than a few champion kills because of the immense lane pressure that Super Minions will provide, as well as all minions in other lanes.
Unlike turrets, inhibitors do not gain any armor or magic resistance when no enemy minions are within its sight range.
Damage with autoattacks to inhibitors is based on your base attack damage plus either bonus ad or 40% of ap, whichever is higher.
The Inhibitors were sometimes referred to as "Barracks" (e.g. in detailed statistics), the name of a similar building in DotA.