iTTi Gloss: Adware

A software package that automatically plays, displays or downloads advertising material to a computer after the software is installed on it or while the application is being used. 

From ISACA Glossary 

Adware is free software that is supported by advertisements. Common adware programs are toolbars that sit on your desktop or work in conjunction with your Web browser. 

From TechTerms 

Adware, or advertising-supported software, is any software package which automatically renders advertisements in order to generate revenue for its author. 

From Wikipedia 

Adware permeates vary many instances of application SW and SaaS (SW as a Service) and accordingly our own lives. Unless voluntarily installed or tolerated it is considered malware of diverse or unknown severity ranging from a nuisance or pain in the neck to spyware or other sorts of Trojans. 

It is important that adware features are scrutinized in detail and published so that users are aware of the toll they pay and the exposures to which they are subject. No need to say that stealth malware may be even worse.