Query Explorer for Analytics
Google Analytics Core Reporting API v3
Google Analytics Segments (for API v3)
Explains the terms Users, Sessions, Hits and their relation to segments.
Gives examples on conditional segments and how these conditions are applied to segmetns.
Explains dynamic segments, more complex conditions as well as operators for advanced conditions.
Also gives a list about which metric can be applied to Users, Sessions and Hits.
Provides a list of default API segments and their ids.
Documentation on how to get a list with all default and customized segments that are usable by an account.
Google Analytics filters (for API v3)