Pronunciation: 'o-"sh&ks
Function: adjective
Date: 1951
Definition: being or marked by an unsophisticated, self-conscious, or self-effacing manner. Mirriam Webster's Collegiate Dictionary

"Aw-shucks" is a common expression often used when people are not sure how to respond to a compliment and do not wish to appear conceited. It suggests that the person being complimented is embarrassed but flattered nonetheless.