MetaTables

Meta tables allow you to add functions to all classes in the game at the same time.

For example, adding a function to "Entity" meta table like so:

Will allow you to use it on ALL entities like so:

However adding a function like this:

Will not allow you to use that function on any other entity BUT Entity( 1 )

A list of type meta tables that can be retrieved with FindMetaTable can be found on TYPE enum.

Derived Metatables

In GMod, any C class that is derived from another has the field MetaBaseClass defined in the metatable, which points at the derived metatable. An example for this would be: