A specific type of spyware that will allow a hacker or malicious perpetrator to spy on the infected computer’s Internet browsing activity. Using a browser hijacker the person responsible for the spyware can deliver pop-up ads, reset the browser homepage, or direct the browser to Web sitesthe victim would not normally visit.
See The Difference Between Adware & Spyware in the Did You Know? section of Webopedia.
Also see All About Web Browsers in the Quick Reference section of Webopedia.