A lot of programs--especially free ones--install additional software on your PC. They do this as a form of advertising, and they may make some money off of it. Of course, it can backfire and alienate users. Read More ..
This practice gives you, the user, an additional responsibility. If you're not careful about how you install freeware, you can end up with a lot of potentially unwanted programs (PUPs).
(Frankly, giving what we're talking about, I find that acronym way too cute and cuddly. The acronym would have been far more descriptive if everyone had agreed on the term "potentially unwanted software." On the other hand, these programs leave messes all over your PC, so perhaps PUP is appropriate.)