The word malware is short for “malicious software.” Malware is any software designed to cause damage to a computer, server, or computer network and perform different kinds of operations without the owner's permission.
There are a lot of different types of malware. Every type has their own way of causing some form of damage to your computer.
The rest of the information on malware and its history is here:
What is malware? & here
What is malware?