What is the .git suffix for in respositories URLs?

Both HTTPS access and SSH access is using a .git suffix (in the HTTPS URL it is optional).

What is it for?
What is the reason it was added?

Thank you, Sela

Welcome to the community!

The .git denotes a Git file extension for downloading repositories. Some urls do not have that extension, but can still be used to clone repositories.
Here’s another post to give a bit more context.