Ich werfe mal noch das BGG-Glossar in die Runde (soweit man das als Quelle akzeptieren mag):
abstract
adj. Generally means simplified instead of detailed. In the context of games, it is an overloaded term which usually means "without theme or story" or "not highly detailed; simple, elegant rules without lots of chrome" but "abstract" also sometimes used to mean "pure strategy (no randomness)" Often used as opposite of thematic. See the term abstract strategy game and article Abstract Strategy.
abstract strategy game
1) A game generally limited to two players and perfect information (i.e. no randomness) often with incidental or irrelevant theme. (Chess does have a theme, but it can be ignored. A bishop is just the name of a piece that moves diagonally.)
2) A game with no theme.