"Cap" is applicable only if you are raising via a convertible note. If you are doing an equity round (issuing new stock (called a primary, is most normal) or selling existing stock (called a secondary) then you wouldn't talk about a cap but a "valuation" instead (pre or post money).

In that context a cap is short for a valuation cap, meaning the highest possible valuation that will be used to calculate the conversion of the note to stock during the next fundraise in which stock is issued.

A note is like a promise to give you stock in the future in exchange for your money now.