It could be going to a baby shower, buying someone lunch, or turning in your research paper by Tuesday. If you have to do it — even if you'd rather not — then you’re obligated.
Obligated can mean that you have to do something because the law or the rules say that you do. For example, you’re obligated to pay your taxes by April 15. It can also mean that you just feel like you need to do something because it’s the right thing to do or because you feel like you owe someone. You’re obligated to go to your best friend’s birthday party, even though you’d rather be out with your new boyfriend.