Nagware (also known as begware, annoyware or a nagscreen) 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 intermittently while the user is using the application. These messages can appear as windows obscuring part of the screen, or as 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 is generally that the user will register or buy the program to get rid of the trial version's annoyance.