Inhibitor

The Inhibitors are the buildings that block the training of enemy Super Minions in the same lane. For example, once an enemy team's inhibitor is destroyed, the Nexus will start spawning super Minions, along with regular Minions, in the corresponding lane. Once the said Inhibitor respawns (after a certain amount of time), super Minions will no longer spawn. Inhibitors are usually protected by a turret which can make destroying them difficult.

Trivia

 * The Inhibitors are sometimes referred to as "Barracks" or "Rax". This is what a similar building in DotA is called.