Introduced in Patch 7.2.0, Blizzard's API documentation groups related functions, events and tables into namespaces or systems which have one of the following names:

• namespace - Begins with C_ and, increasingly in recent expansions, may be the global name of a lua table containing functions.
• system - Used primarily by /api hyperlinks for the in-game API documentation and may be similar to the FrameXML filename.

The system name is often, but not always, same as the namespace after stripping C_. Subcategories below are titled after namespaces, whether officially named or implied.