But what is computer science? It sounds simple enough—computer science is a branch of science that studies computers. But not everyone who works with computers is a computer scientist. The use and development of computers comprises a number of overlapping disciplines.
Before these disciplines are discussed, you need to understand a few terms.
A program is a series of steps to accomplish a given task. In general usage, a program might refer to everyday instructions, written in English, such as instructions to change a tire or register for a college class. In computer science, however, the term “program” refers to a series of steps given to a computer.
A computer is an electronic device for performing logical and mathematical operations based on its programs. The term includes not only the obvious electronic devices that have a screen, keyboard, printer, and so on, but also computers that are embedded into devices like those at supermarket checkout counters or in DVD players. What makes computers interesting and powerful is that they can be given arbitrary sets of instructions to perform.
Hardware refers to all the physical devices that make up a computer system, both those inside the computer “case” and those outside the case, like monitor, keyboard, and mouse.
Software refers to the programs the computer executes. For example, the word processor Microsoft Word, or the computer game “Half-Life,” is software, as is a program that enables a cell phone display so the user can select a new ring-tone. By analogy, when you play a movie in a DVD player, the movie is the software and the player is the hardware.
A programmer is someone who creates programs.
User refers to a person who uses a software program or computer.
Source of Information : Broadway-Computer Science Made Simple 2010