Almost all of us have to prove to the computer that we are who we say we are. Normally that’s done with a username and a password. Entering these in correctly and getting access to the computer is known as logging in, and typically these credentials are called your login details.
This is very popular operating system which was originally developed by Linus Thorvalds in the 1990s: he still leads the way on development of it. In terms of software used in corporate machines it’s probably second after Microsoft, ahead of Apple’s MacOS.