MIME stands for Multipurpose Internet Mail Extension. It is an add-on or a supplementary protocol which allows non-ASCII data to be sent through SMTP. It facilitates the exchange of data files on the internet and was proposed by Bell Communications in 1991.

In the context of .NET and web development, MIME stands for Multipurpose Internet Mail Extensions. MIME is a standard that extends the format of email messages to support text in character sets other than ASCII, as well as attachments of audio, video, images, and application programs.

In the context of .NET, MIME types are also used to specify the type of content being sent in HTTP requests and responses. For example, when a web server sends a response to a browser, it includes a MIME type in the response headers to indicate the type of content being sent (e.g., text/html for HTML content, image/jpeg for JPEG images, etc.).

In .NET, you can work with MIME types using classes and interfaces provided in the System.Net.Mime namespace, such as ContentType and ContentDisposition. These classes allow you to work with MIME headers and content types programmatically.