Adware is free software that is supported by advertisements. Instead of generating revenue through sales, an adware developer sells online ads that appear while the app runs. The developer may also sell an upgraded ad-free version of their software to users who want to use the app without ads.
Smartphone and tablet applications frequently use an adware model. Apps may include a small banner ad while you use them to provide some revenue for the developer. Some apps, particularly mobile games, may require that you watch a short video ad between uses or game levels. An in-app purchase is often available to remove ads for a one-time purchase or recurring subscription.
Most adware is safe to use, but some may inject ads into other parts of the operating system's user interface, serving as a form of malware. These ads may appear as popups or as extra ads injected into webpages. Ads introduced by malware may be difficult to remove, appearing even after the adware that introduced them is uninstalled. You may need to use antivirus and antimalware software to completely remove malicious ads.