Malware

Malware is just software that was written to do something to your computer that you did not ask for and would not agree to.

It is a category rather than a specific thing, in the same way that "vehicle" is. Some of it steals passwords. Some watches what you type. Some quietly uses your machine to attack somebody else. Some locks your files and asks for money. What they have in common is only that somebody else decided what your computer should do. It usually arrives the same few ways: an attachment, a download that was not quite what it claimed, or a program that came bundled with something you did want.