A computer in the modern sense is a technological device that can store digital information, transform the information (via programming) and output the information in a number of different ways ( on screen/printing/movement). 

Computers rely on a wide range of electronic components to do all these functions.  

On a basic level a computer consists of a central processing unit (CPU), memory (volatile vs non-volatile like flash memory), input devices and output devices.


A typical personal computer set up.  image: Apple

Computers today are integral to to everyday functioning of the modern world. In particular millions of computers are connected to each other to produce the Internet.

Computers come in a variety of scales or sizes for various purposes from handheld computers usually called smart phones, or tablets, laptops, desktops to larger scale supercomputers.  Traditionally though the term computer generally meant a desktop or a laptop scale device.