A holiday is a special day reserved to honor some notable figure or event. It can also to refer to a series of days. Lua error in package.lua at line 80: module 'Module:Inlinegfx/img_link_data.json' not found. Patch 7.1.5 introduced a shorter version of these types of events (although some previous holidays were very short) called Micro-holidays.
Many events in World of Warcraft celebrate various holidays mostly based on those celebrated in Azeroth, but trappings of these holidays can also appear in Outland.