URL encoding is a technique used to convert characters in a string into a format that can be safely used in a URL. The process of URL encoding involves replacing certain characters with percent (%) signs followed by two hexadecimal digits. For example, the character "#" is replaced with "%23", and the character " " (space) is replaced with "%20". This ensures that all characters in the URL are properly encoded and that the URL can be safely used in conjunction with other URLs. URL encoding is often necessary when submitting form data to a server, as many characters are not allowed in URLs. When using URL encoding, it is important to ensure that all unencoded characters are valid for use in a URL. Invalid characters will be automatically encoded by most browsers, but this can lead to incorrect or invalid URLs.