Base64
In plain terms
An encoding that represents binary data as ASCII text.
Going deeper
Base64 converts binary into a text-safe representation so it can travel through text-only channels like email or JSON. It encodes, not encrypts.
Under the hood
Increases size ~33%; not security, just safe transport of binary in text contexts.
Examples
Email attachments, data URIs, encoding images in JSON, JWT parts.
Think of it like...
Like spelling out a picture in letters so it survives a text-only telegram.