An appraisal is a judgment of something, especially an estimate of how much it's worth. Usually you need an expert to give an official appraisal.
If you were selling a house, you'd need an expert in real estate to give an appraisal of how much it's worth — that's an official estimate of how much you could sell it for. But this word can also be used in other less formal situations that call for a judgment or opinion of some sort. If you painted a picture, you could ask, "What's your appraisal of my work?" Hopefully the answer is "beautiful!"