"?", ascii character 63.
Common names: query; itu-t: question mark; ques. Rare: whatmark; intercal: what; wildchar; huh; hook; buttonhook; hunchback.
Question mark is used, along with colon for c's lazy triadic "if" operator (similar to the iif function in visual basic). The expression x?y:z evaluates x, then if x is true it returns y else it returns z.
In unix shell file name patterns, question mark matches any single character.