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"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.
Idle talk; blathering (1782+)
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.