Percent-encoding is a way of encoding information in a URL, which is like an address for a website. It means taking letters, numbers, and other characters and changing them into a code using the symbol '%' followed by two numbers. For example, let's say you wanted to write the letter 'a' in percent-encoding. The code for 'a' is '%61'. Using percent-encoding, websites are able to store and share more complicated information in a URL.