Under Linux, there is a well-known expression:
On a Linux system, everything is a file; if something is not a file, it is a process.
While this is not strictly 100% true, it is true for at least 90% of things you will encounter on Linux, definitely if you're not very advanced yet. Even though, in general, this rule works out, it has some extra notes. While most stuff on Linux is a file, there are different file types, seven to be exact. We'll discuss them all in the coming pages. You will probably not use all seven; however, having basic knowledge about them all gives you a better understanding about Linux in general, something which is never a bad thing!
