Spyware
Spyware' is a category of software for computers. Spyware is software that collects some data, usually without the computer users' knowledge. Very often, this data is then sent over the internet to a third party, which can use it for something. Very often, this is used for marketing. But spyware can also  be used to get data from computers that they should not know. It can be used as a keylogger which can see what you are typing into the Internet. Keyloggers can steal important information like passwords that you type.