1. Intended, expected, or believed to do something. This new software is supposed to make things a lot more efficient, but I find it so confusing that everything is taking me twice as long! We're supposed to arrive around 3 PM, assuming our flights aren't delayed.

2. Required or obligated to do something. I was supposed to be home an hour ago—my parents are going to kill me! Please don't distract him, he's supposed to be cleaning his room.

3. Allowed or permitted to do something. (Chiefly used in questions and negative constructions.) You're not supposed to go in there! Are you sure you're supposed to be in here?