(general term): One of the most popular encoding schemes in use today. It is used to translate binary data that includes nonprintable characters in a printable format to be able to transmit this data with text-based protocols such as SMTP (email) or HTTP (Web).
Note that encoding is not equivalent to encrypting. Encoding just transcribes the data in a different alphabet and involves no keys. The transmitted message can still be considered clear text and is, in fact, picked up directly by network sniffers.