Tody i tell you
What is mime types
MIME type is fancy word for different types of files.
All files have a "file extension" like .mp3
or .wav .mov .avi etc.
.mov is the quicktime MIME type.
I would just click the NO button. Quicktime is annoying I believe its actually a Native Mac program on windows. Also if other programs ask this, it means that it wants Default over that file extension. Say iTunes asks that, it means it wants to be the default player for any .mp3 files you have. So when you double click the .mp3 it will launch itunes
