Base64 is an encoding that represents binary data using 64 printable characters (A-Z, a-z, 0-9, + and /), with = used for padding.
Why it matters
It lets binary data travel through text-only channels such as email or JSON. It is not encryption: anyone can decode it. Output is about a third larger than the input. Example: “Hello” becomes “SGVsbG8=”.
Source: RFC 4648