OS - essential that allows a computer to be useful , manages hardware and the user interface.Most important in any computer system controlling time a task takes in processor , retrieving data from storage , monitoring input and output
Single user OS - An operating system that allows a single user to perform only one task at a time is called a Single-Tasking Operating System. Functions like printing a document, downloading images, etc., can be performed only one at a time. However you can do single user multi tasking where you can do multiple tasks at the same time
Multi user OS - A multi-user operating system (OS) is a computer system that allows multiple users that are on different computers to access a single system's OS resources simultaneously, as shown in this figure appearing on your screen right now. Users on the system are connected through a network. For example a mainframe computer allows many different users to run off the mainframe computer