Apple designates a number of different Media Types (mt values):
1 Music
2 Podcasts
3 Audiobooks
4 TV Shows
5 Music Videos
6 Movies
7 iPod Games
8 Mobile Software Applications
9 Ringtones
10 iTunes U
11 E-Books
12 Desktop Apps
So, to answer your question, the “mt=8” in iTunes links simply identifies it as being of type ‘Mobile Software Applications’.