A general term for a program that surreptitiously monitors your actions. While they are sometimes sinister, like a remote control program used by a hacker, software companies have been known to use spyware to gather data about customers. The practice is generally frowned upon.
blackice.iss.net/glossary.php

A technology that assists in gathering information about a person or organization without their knowledge. On the Internet, "spyware is programming that is put in someone's computer to secretly gather information about the user and relay it to advertisers or other interested parties." As such, spyware is cause for public concern about privacy on the Internet.
reach.ucf.edu/~coursdev/cdrom/html/help/glossary.html

This is also known as "adware". It is a hidden software program that transmits user information via the Internet to advertisers in exchange for free downloaded software. The Specialty Alliance Corporation\ufffd does NOT use Spyware in any form or fashion, or will do business with companies that do.
www.calnique.com/glossary.htm

There are concerns that some Web sites and commercial organisations track users' online activity through the use of what is called \ufffdspyware'. Usually coming in the form of \ufffdcookies' - these enable the cookie writer to build-up information about what you do and where you go on the Web. Software is available that checks for and removes spyware.
www.btsafersurfing.com/glossary/p_t.html

Software that tracks usage and reports it to others, such as advertisers Usually the tracking is concealed from the user of the software.
www.cba.nau.edu/facstaff/durham-j/glossary_orphanware.htm

Simply speaking, spyware consists of hidden programs running on your computer. You may have unknowingly installed them when you downloaded programs from the Internet or installed software from disks. These programs are easy to install but often difficult to remove without downloading specialized anti-spyware programs.

Spyware programs can change your system settings, serve pop-ups, record your surfing habits, or display advertisements over web sites you visit. Other spyware programs will run separate programs on your computer for a variety of purposes, sometimes slowing your computer down in the process. Some malicious spyware will log everything you type on the keyboard and even send this information back to those who placed the spyware on your computer in the first place. This could be embarrassing at minimum, and even result in your becoming a victim of identity theft.