Dropper

The dropper is a block that drops an item from its inventory as an entity (as if it was dropped by the player) each time it is powered. If there is a chest immediately in front of the dropper when it is powered, it will instead store the item within. A dropper can drop items through a glass block in front of it.

This is in contrast to a dispenser, which behaves differently with certain items, such as firing projectiles, placing liquids from buckets, and spawning mobs from spawn eggs. Dispensers also do not store items in chests.

Trivia

 * By placing droppers so that they feed into each other, similar to a hopper pipe, and powering them each with comparators, Minecraft's fastest item transport system can be produced, with the advantage of going all 6 directions, at a speed of 20 blocks per second. This means that if you have a 100 block long dropper pipe, items going in on one end will pop out the other end in only 5 seconds.