“Computer” is not an acronym, it is a word derived from a word “compute” which means to calculate. So, in simple words you can say that computer is an electronic device which is used for fast calculation.
Some people say that COMPUTER stands for Common Operating Machine Purposely Used for Technological and Educational Research. It is only a myth because first this definition does not make any sense and second when the computer were invented they were just calculating machines which needs a lot of space for establishment.
A computer is a machine that can be instructed to carry out sequences of arithmetic or logical operations automatically via computer programming. Modern computers have the ability to follow generalized sets of operations, called programs. These programs enable computers to perform an extremely wide range of tasks. A “complete” computer including the hardware, the operating system (main software), and peripheral equipment required and used for “full” operation can be referred to as a computer system. This term may as well be used for a group of computers that are connected and work together, in particular a computer network or computer cluster.