premise: the <mask> of a piano, an organ, an accordion, a computer keyboard, or of a typewriter.
hypothesis: the best context for <mask> here is One of a set of small movable parts on an instrument or machine which, by being depressed, serves as the means of operating it; but not A word or other combination of symbols which serves as an index identifying and pointing to a particular record, file, or location which can be retrieved and displayed by a computer program; .  When the key is a word, it is also called a keyword..