What's the "een" in Halloween?
"pinch, pluck, twist," usually to the nose, probably from Old English twiccian "to pluck," of obscure origin; perhaps related to twitch. Meaning "to make fine adjustments" is attested from 1966. Related: Tweaked; tweaking. The noun in this sense is recorded by 1989.
[perhaps a memory of the days when a crystal was tweaked with a ''cat's whisker'' in order to tune a primitive radio receiver]
1. To change slightly, usually in reference to a value. Also used synonymously with twiddle. If a program is almost correct, rather than figure out the precise problem you might just keep tweaking it until it works. See frobnicate and fudge factor; also see shotgun debugging.
2. To tune or bum a program; preferred usage in the UK.