Real Dictionary

shrug
verb: If you shrug, you raise your shoulders to show that you are not interested in something or that you do not know or care about something.

shrug in American English
the gesture so made
to draw up (the shoulders), as in expressing indifference, doubt, disdain, contempt, etc.
intransitive verb: to raise and contract the shoulders
transitive verb: to raise and contract (the shoulders), expressing indifference, disdain, etc

shrug in British English
noun: the gesture so made
verb: to draw up and drop (the shoulders) abruptly in a gesture expressing indifference, contempt, ignorance, etc