A DiscriminatedUnion introduced by MicroSoft's ComAutomation.
The Variant DataType is a struct consiting of a member "vt", which contains the enum for the type currently stored in the Variant, and a union who's largest member is a decimal stored as a 12 byte unsigned integer scaled by a variable power of 10. Thusly, a Variant is always costs you 16 bytes at minimum.
Variants are used by ScriptingLanguages because they are typeless. However, Variants also are used as a form of enabling overloading for an property/method in an interface.
Actually, Variants are used by typeless ScriptingLanguages. Some aren't typeless. --PierrePhaneuf
Note: The actual TypeName is Variant, but that's not a valid WikiName.
VC++ has a non-heinous wrapper called _variant_t.