MIME
In plain terms
A standard indicating the type of content in a message.
Going deeper
MIME types label data formats (like text/html or image/png) so software knows how to handle content in emails and HTTP. They declare what the data is.
Under the hood
Sent via Content-Type headers; browsers and clients use them to render or download appropriately.
Examples
Content-Type headers, application/json, image/png, email attachments.
Think of it like...
Like a label on a package telling the recipient what's inside and how to handle it.