What is a Debuff in WoW? World of Warcraft Terms

For many new players of the game World of Warcraft, the term “debuff” often makes little sense. This term simply means a spell or ability that applies a hostile effect on an enemy or on yourself that lasts for a time. For example a Curse of Agony spell lasts for about 30 seconds, dealing damage every few seconds, making it a debuff. A Shadow Bolt on the other hand deals its damage instantly, and so it is not a debuff. A debuff is the opposite of a buff, and may or may not be a DoT.
Ever wonder what a debuff is?