When you decode something, you figure out its meaning by translating it from a code, cipher, or unfamiliar form into something you can understand. If someone sends you a message written in a secret code where each letter is replaced by a number, you decode it by converting those numbers back into letters to read what it says.

Reading is actually a form of decoding. When you first learned to read, you had to decode each word by sounding out the letters: seeing the marks C-A-T on a page and realizing they represent the furry animal that purrs. Beginning readers spend a lot of effort on decoding, while experienced readers recognize most words instantly.

Scientists decode data to understand what it means. Cryptographers during World War II worked to decode enemy messages to learn their military plans. When your friend gives you a funny look across the classroom, you might try to decode what they're trying to tell you without words.

The opposite of decode is encode, which means putting information into code in the first place. If you and a friend create a secret language where you speak in Pig Latin, you're encoding your conversation so others can't easily understand it.