Programs are instructions that tell the CPU what to do. Programs are fundamentally the same as data. The CPU needs to be told which is which--it can't tell the difference otherwise. A program is really just a bunch of special codes that tell the computer what operation to perform.
1. The Operating System (OS) is a program that allows the computer to run user programs. It brings the computer to life because it tells the computer how to do things—read a disk, run a program, read the keyboard, run the screen, network, etc. The OS is always running and never goes away. DOS, OS/2, Windows, MacOS, VMS, UNIX, etc. are examples of operating systems.
2. User programs tell the computer what to do with things the OS has taught it to do. These are the programs that really do the useful work. Microsoft Word, Excel, Lotus 123, WordPerfect, etc. are examples of user programs.