What is a Pally in WoW? World of Warcraft Terms

Many beginning players of the MMORPG World of Warcraft have heard the term “pally” and been puzzled over its meaning. Pally simply refers to the paladin player class. Most people use it as an abbreviation, or because they like the sound of it better than Paladin. It can be used to make compound terms such as “pally tank”.
Ever wonder what a "Pally" is?