Prerelease and unused content

Beta is something that is changed or not in the final version of a game. This information is usually given out before the game's release, or data left in the game's coding that is not seen through normal gameplay. There are not as many beta elements in the Animal Crossing series as there are in others, though.

Examples
Many games have beta elements. One example is in the game New Super Mario Bros. Wii. For those who have not played the game, there's an item called the Propeller Shroom. While it is an orange mushroom with yellow spots and a propeller sticking out of it now, originally, it was a red "P" with a propeller on top of it when shown at the 2009 E3 presentation.

In Animal Crossing
There are very few beta elements in the Animal Crossing series. One of the beta items is a sickle.