What does the grey dotted circle next to a song in iTunes mean?

I put some new music in my iTunes library and for some reason it won't sync onto my iPhone. When I click the "On This iPhone" tab and go to my Recently Added all the songs are there but they're grayed out and have this dotted circle to the left of the name. For whatever reason they just won't sync to my phone no matter what. I've restarted my phone, computer and iTunes but nothing works. I appreciate any help! Thanks.

The source file of the music in the computer may be deleted, you have to redownloaded them again.

Wrong. That is the full grey circle with the exclamation point in it. As for the dotted circle, I am having the same problem and no one seems to have the right answer.