Definitions of Spyware on the Web:

The following definitions are from various sites devoted to spyware discovery and removal.  I suggest following the links, at the bottom of the page, if you want to know more.  Also, go here for the most comprehensive list of spyware currently circling the internet:

http://www.spywareguide.com/

Spyware is 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.

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.

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. 

There are concerns that some Web sites and commercial organizations track users' online activity through the use of what is called ‘spyware'. Usually coming in the form of ‘cookies' - these enable the cookie writer to build-up information about what you do and where you go on the Web.

Software that tracks usage and reports it to others, such as advertisers Usually the tracking is concealed from the user of the software.

Links for more information on the above mentioned definitions:

http://blackice.iss.net/glossary.php
http://reach.ucf.edu/~coursdev/cdrom/html/help/glossary.html
http://www.btsafersurfing.com/glossary/p_t.html