If you're on this page, I probably used a term you don't understand. This glossary will attempt to explain any term related to A Link to the Past in an easy-to-understand vocabulary.
(pl. ancillae) Along with NPCs and garnish, ancillae are one of the 3 major types of self-acting entities. There are 10 available slots for ancillae, which tend to be objects created by an action Link performed. For example, the boomerang is an ancillae created by using the boomerang item. When you press Y, that ancilla comes into existence, and from there, it executes its code on its own every frame until it is no longer active.
Along with ancillae and NPCs, Garnish are one of the 3 major types of self-acting entities. There are 30 available slots for garnish, and they mostly act as a miscellaneous extension of sprites. For the most part, if you see some sort of sparkle or debris coming off of a sprite, it is likely garnish. Some examples are the circles trailing the leader when Mothula fires a beam, or the sparkles you see on frozen enemies.
Garnish can't interact with Link, which explains why he takes no damage from the tail of a fire snake or laser beam. Those graphics are created as garnish.
To quote Dotsarecool:
This is gonna sound a little pedantic, but that's because it is.
The general term you will hear for this word is sprite. While there's nothing wrong with that in a normal conversation, it can cause confusion when you want to discuss more technical aspects of the SNES, where sprite has other meanings. To remove all ambiguity, I may instead be use the term NPC, a term which shouldn't be unfamiliar to most. If there are no graphics to discuss, I'll probably stick to saying Sprite. Moving on…
Along with ancillae and garnish, NPCs are one of the 3 major types of self-acting entities. There are 16 available slots for NPCs, and they're mostly the bad guys you beat up or the people you talk to. For example, Ganon is an NPC. Some NPCs are used for more specific purposes, such as tree pulls, which only appear on certain objects, or the arrow target for the moving wall in Palace of Darkness.