Older people in the Southern United States sometimes use "mash" as a verb meaning "to press". The word is usually uttered in such a strong Southern accent that a neophyte Yankee can't possibly understand it. For example, if you're in an elevator next to the buttons and a kindly old gentleman gets on, he may well say:
"Mayush fo', ee-ya wuh."
which, without the accent, is
"Mash four, if you would,"
which, when translated, means
"Would you please push the 'four' button?"
The term usually takes something like a button or a switch as a direct object; one could conceivably mash a computer key, too, although most people who use this term don't seem to be the computer-literate sort. "Mash" does not take on all the senses of "press"; one does not mash a garment, nor does one mash against someone.
There. Now if you're ever in an elevator in Dixieland, you'll know what to do.
melknia tells me that some young Canadians use "mash" in this sense. So I modify my above statement: if you're north or south of the American North, you'll hear the word used this way. Strange...