Nagware is a term of distinction used to differentiate between types of shareware software. Other types of shareware include demoware, crippleware, freeware, adware, and even spyware.

Nagware (also known as annoyware) is a type of shareware, that reminds —or nags— the user to register it by paying a fee. It usually does this by popping up a message when the user starts the program or, worse, intermittently while the user is using the application. These messages can appear as windows obscuring part of the screen or message boxes that can quickly be closed. Some nagware keeps the message up for a certain time period, forcing the user to wait to continue to use the program. The intent, of course, is that the user will become so annoyed with the messages that he/she will register it just to get rid of them.