The word crop has several meanings:

1. Plants grown by farmers for food or other uses. Wheat, corn, and soybeans are major crops in the American Midwest. A farmer might plant different crops each season, rotating between vegetables one year and grains the next. When you hear about a bumper crop, that means an especially large and successful harvest. The word can also refer to the harvest itself: “This year's corn crop was excellent.”
2. To cut something short, especially the edges of a photograph or someone's hair. When you crop a photo, you trim away parts you don't want, keeping only the best portion. A barber might give someone a close-cropped haircut, cutting the hair very short. Artists crop their drawings to focus attention on the most important parts.
3. A short whip used in horseback riding, also called a riding crop. Riders use it to give light taps as signals to the horse.

The phrase cream of the crop means the very best of a group, like the top students in a graduating class.