Content-Type is an HTTP header used to describe the type of data being sent or received in a web transaction, such as in requests and responses. This header helps the browser or server understand how to process the content of the message body (e.g., whether it is plain text, HTML, JSON, or an image).

The Content-Type header is typically associated with MIME types, which define the format of the data. The file extension corresponds to the format or type of the file, which helps identify how the file is to be interpreted or rendered.

Common Content-Type values and their associated file extensions:
Text-based content types:

Content-Type: text/html

File Extension: .html, .htm
Represents HTML documents.
Content-Type: text/css

File Extension: .css
Represents CSS (Cascading Style Sheets) files.
Content-Type: text/javascript

File Extension: .js
Represents JavaScript files.
Content-Type: text/plain

File Extension: .txt
Represents plain text files.
Image-based content types:

Content-Type: image/jpeg

File Extension: .jpg, .jpeg
Represents JPEG image files.
Content-Type: image/png

File Extension: .png
Represents PNG image files.
Content-Type: image/gif

File Extension: .gif
Represents GIF image files.
Content-Type: image/webp

File Extension: .webp
Represents WebP image files.
Audio and Video content types:

Content-Type: audio/mpeg

File Extension: .mp3
Represents MP3 audio files.
Content-Type: audio/wav

File Extension: .wav
Represents WAV audio files.
Content-Type: video/mp4

File Extension: .mp4
Represents MP4 video files.
Application-based content types:

Content-Type: application/json

File Extension: .json
Represents JSON (JavaScript Object Notation) files.
Content-Type: application/xml

File Extension: .xml
Represents XML files.
Content-Type: application/pdf

File Extension: .pdf
Represents PDF (Portable Document Format) files.
Content-Type: application/octet-stream

File Extension: .bin, .exe, .dll, etc.
Represents binary files (often used for non-specific file types).
Content-Type: application/zip

File Extension: .zip
Represents ZIP archive files.
Content-Type: application/x-www-form-urlencoded

File Extension: None (Used in form submissions)
Font-based content types:

Content-Type: font/woff

File Extension: .woff
Represents Web Open Font Format files.
Content-Type: font/woff2

File Extension: .woff2
Represents Web Open Font Format 2 files.
Multipart content types (used for handling multiple parts of a message, such as file uploads):

Content-Type: multipart/form-data

File Extension: None (Used when forms are used for file uploading)
Content-Type: multipart/alternative

File Extension: None (Used for email with multiple versions of content)
Examples:
HTML document:

Content-Type: text/html
File Extension: .html or .htm
CSS file:

Content-Type: text/css
File Extension: .css
JSON response:

Content-Type: application/json
File Extension: .json
Image (JPEG):

Content-Type: image/jpeg
File Extension: .jpg or .jpeg
PDF document:

Content-Type: application/pdf
File Extension: .pdf
Conclusion:
The Content-Type header helps web browsers and servers understand how to handle the data being exchanged. It often maps to a specific file extension that reflects the format of the content. By using the right Content-Type, servers can ensure that content is properly displayed or processed by the browser or application receiving the data.