base64

A text-based data encoding that allows binary data to be sent over channels which only support ASCII text (e.g. teletype systems), at the cost of a 33% increase in size. Standardized by RFC 4648. Often recognizable by the presence of one or two equals signs (=) at the end of the text, though this is not possible when padding characters are ommitted, or when the length (in bytes) of the original data is a multiple of 3.

YouTube notably uses a form of this encoding - specifically "Base 64 Encoding with URL and Filename Safe Alphabet" (RFC 4648 §5) - for its video IDs, with padding characters ommitted. For example, dQw4w9WgXcQ is the video ID for Never Gonna Give You Up.

More recently popularized by Doki Doki Literature Club, which used Base64 in several of its easter eggs.