Digest has two main meanings:

1. To break down food in your body so it can be absorbed and used for energy. After you eat lunch, your stomach and intestines digest the food over several hours, turning it into nutrients your body can use. Some foods are easier to digest than others: a slice of bread digests more quickly than a tough piece of meat. When you have an upset stomach, you might say your food isn't digesting well.
2. To think through information until you really understand it. When your teacher explains a complicated math concept, you might need time to digest what you've learned before you can use it. After reading a surprising news story, you might say “I need some time to digest this” because you want to think it through carefully. Just like your stomach breaks down food into smaller parts, your mind breaks down complex ideas into pieces you can understand.

The word digest (pronounced DYE-jest when used as a noun) can also mean a short summary of a longer text, like a magazine called Reader's Digest that offers condensed versions of articles and stories.