YoAngels is a term that began on the YoWorld Forums a bit after the wishlist thread began. What it means is simply a player who loves to gift other players out of the kindness of their hearts. They grant the wishes of many who post on the wishlist thread, which can be found under the Wishlists and Giveaways category at YoWorld's Official Forums.
Although they have been around since the start of the game, most of them began to appear when the wishlist threads began to come into place on the forums. All the gifting and generosity caused more people to do the same.