Itunes -- Why are about 2/3 of my songs checked off in my music library?

[GIZBUG]

Every time I open my itunes up, it goes to my Library/Music.
All my songs are listed there, and about 2/3 of them have checks in the check mark column. My question is, what does this check mean, and why are they checked? I thought maybe they were the ones I uploaded to the cloud for itunes match, but I matched my entire library,

 

[r.j.s]

Check means active. If a song is unchecked, it won't be played (unless specifically selected) or synced to an iPhone/iPod/iPad.

 

[GIZBUG]

Check means active. If a song is unchecked, it won't be played (unless specifically selected) or synced to an iPhone/iPod/iPad.

Ok, if I remove the check, it removes it from my library list which is weird ?