[Usenet] The variety of shareware that displays a large screen at the
beginning or end reminding you to register, typically requiring some sort
of keystroke to continue so that you can't use the software in batch mode.
Compare annoyware, crippleware.
The Free On-line Dictionary of Computing (30 December 2018):
/nag'weir/ A term, originally from Usenet, for the
variety of shareware that displays a message on start-up and/or
termination reminding you to register, pay or donate (see
Sometimes user interaction is required to dismiss the nag in order
to use the program, making it useless in batch mode.
Nagware may also be crippleware, with a message nagging you pay
to upgrade to the full or "pro" version.