an alphabetical list of words relating to a specific subject, text, or dialect.
An Ad Group is a part of a campaign, which contains one or more ads targeting a shared set of keywords/placements/topics/interest or remarketing list. One can create 20000 Ad Groups in a single AdWord campaign. Adding and removing ads or keywords according to the performance is done in an Ad Group. One can also set prices for individual keywords within an ad group or can organize ad groups by a common theme, such as the types of products or services one wants to advertise.