Real Dictionary

strum
verb: If you strum a stringed instrument such as a guitar, you play it by moving your fingers backwards and forwards across the strings.

strum in American English
the act or sound of this
to play (a guitar, banjo, etc.), esp. with long strokes across the strings and often in a casual or aimless way, or without much skill

strum in American English 1
intransitive verb: to play on a stringed musical instrument by running the fingers lightly across the strings
noun: the act of strumming
transitive verb: to play on (a stringed musical instrument) by running the fingers lightly across the strings

strum in American English 2
noun: a strainer, as at the inlet of a system of tubing

strum in British English
verb: to sound (the strings of a guitar, banjo, etc) with a downward or upward sweep of the thumb or of a plectrum