A Potentially Unwanted Program (or PUP) is a program that may be unwanted, despite the possibility that users consented to download it. PUPs include spyware, adware, and dialers, and are often downloaded in conjunction with a program that the user wants. Some PUP files will download taskbars. 
The term was created by McAfee because marketing firms objected to having their products called "spyware": in the view of such firms, all the information necessary for informed consent is included in the download agreement. It is widely recognized, however, that many if not most users fail to read a download agreement in sufficient detail to understand exactly what they are downloading. For instance if the user is downloading a file off of the internet. There's a installer and the user's just clicking through everything and they realize that they've accidentally downloaded something dodgy as well.
The most common type of PUPs are usually rogue software, in which you usually just pay for "removal" of non-existent malware on your computer.
- Potentially unwanted program on Wikipedia.