Stickers versus Emojis: what is the difference?

I have a very basic question. I would like to know the difference between a sticker and an emoji (as used in text messaging). Are they the same thing, our is there a difference? Is it just the size (with emojis being inserted on the same line add the text, and stickers occupying mute space, and below the text)? What about animations, are there both animated stickers and emojis? What is the difference?

Thanks.