"Crop" is a word that you use when you're talking about farming. When someone grows a large number of plants for food, you call it a "crop".

You can talk about a specific "crop" of one kind of plant:

We're expecting to have a really good potato crop this fall.

Or you can talk about all of the "crops" grown by a farmer or a group of farmers:

All of their crops are dying because of the drought.