Spyware is a broad category of malicious software intended to intercept or take partial control of a computer's operation without the user's informed consent.
From : en.wikipedia.org/wiki/Spyware
Any software that covertly gathers user information through the user's Internet connection without his or her knowledge, usually for advertising purposes. Spyware applications are typically bundled as a hidden component of freeware or shareware programs that can be downloaded from the Internet. Once installed, the spyware monitors user activity on the Internet and transmits that information in the background to someone else.
From : www.tjiss.net/glossary_s.html