If you're talking about television shows, soap opera is a subcategory of drama. A soap opera is a show that has an exceptional amount of drama.

Each word can mean several different things. A drama can refer to any theatrical production, whether it is comedy or musical theatre or serious play. A drama can also be a serious (as opposed to comic) theatrical production or a movie. It is usually 2-3 hours long. A soap opera is a kind of drama, usually on television for half an hour a day, that never ends. "The Young and the Restless" has been running for more than 30 years, for example. The topic is serious (in other words, not a comedy), but is overly emotional, sentimental, even ridiculous to its critics. Does that answer your question?