A corpus is a collection of writings. If you tend to never throw anything away, you might have your entire school corpus, from your first scribbled words to your high school English essays.
The written works of an author, or from one specific time period, can be called a corpus if they're gathered together into a collection or talked about as a group. You could discuss the corpus of Dr. Seuss, for example. Corpus sounds a little like corpse, and that's no coincidence; corpus means "body" in Latin, and though it's come to mean specifically "body of work," the two words are closely related.