This is a term used in French cookery. It means a sheet of rolled-out pastry. Abaisser means to roll out thinly.
Sometimes the term abaisse is used for a biscuit (cookie) or a slice of sponge cake, which may be spread with cream or jam.
The word isn’t very commonly used except in the case of French patisserie, so it’s probably not worth making a big effort to commit this one to memory just to expand your vocabulary.