A zombie spawner is a block that can be found in the Nether dimension, or created using a crafting table. When activated, it will spawn zombies at a regular interval. Zombie spawners are often found in dungeons or fortresses, and can be a valuable source of experience and loot.
Zombie spawners can be destroyed using a pickaxe, but they will respawn after a short period of time. The only way to permanently disable a zombie spawner is to use a Silk Touch pickaxe to harvest it. Zombie spawners can be used to create mob farms, which can be used to generate experience and loot.