Real Dictionary

tweak
verb: If you tweak something such as a system or a design, you improve it by making a slight change.
verb: If you tweak something, especially part of someone's body, you hold it between your finger and thumb and twist it or pull it.

tweak in American English
such a pinch
to give a sudden, twisting pinch to (someone's nose, ear, cheek, etc.)
noun: an act or instance of tweaking; a sharp, twisting pull or jerk
transitive verb: to pinch and pull with a jerk and twist

tweak in British English
to twist, jerk, or pinch with a sharp or sudden movement
noun: an instance of tweaking