Is this plaster or sheetrock?

You can tell sheetrock from plaster by rapping on it hard with your knuckles in a couple of places. Plaster will sound solid, while sheetrock will sound somewhat hollow. If it's sheetrock, there is likely to be a wood joist located exactly where the crack is, so it would sound more solid there than if you rapped, say, 8" on either side of it.

However, I do agree with Sammy that it looks like a poorly done sheetrock seam.

It is probably just an appearance issue, and wouldn't involve much ripping and tearing to fix. A competent sheetrock person could probably just cut out the tape and the joint compound on the surface without really damaging the sheetrock much. Then new joint compound and tape would be reapplied. After that dried, several more applications of joint compound would be applied with wider and wider taping knives to feather out the patch.

If its sheetrock, a competent sheetrock person could repair it very quickly and easily. The hard part will be to convince one that its reasonable to accept a job that small. Even a small job requires multiple steps, and there is wait time between as the coats of compound set up. You may have to find a handyman with good skills and let him/her work on it for a while.

Bruce

Before calling in someone, you might try another coat or three of drywall mud over it and on either side, applied with a wide knife and sanded. If it looks respectable after that, prime and paint. It might pop again, but if it were my house, I'd try it.

David-

Just my opinion, but that crack and surface look bad enough that I doubt it can be made to look good with a wide taping knife, especially if the OP has never done sheet rocking before. The tape was improperly applied in the first place, and nothing is going to fix that short of removal.

This is posted in Home Disaster forum and since you've already gotten good info - one thing I can say - its not a home disaster! Just a simple fix - should be easy to hire someone to retape/fix and if you want to watch and learn how to diy, most will oblige.

Smiling :-) because I was once a noob homeowner - weren't we all!