What does a little lock icon next to a file mean?

I transferred music from another computer onto my hdd. now when i open the files on my macbook theres a lock so i cannot import the files into itunes. whats with this?

I think you need to set the permissions in your iTunes. That'd be my guess...add an authorization. I can't remember which menu it's under...just search for it in the help if it's not visible right away.

Rip a track from a cd in itunes and it wont have a padlock.

Buy it from the itunes store and it will have the padlock.

Padlock = DRM protected file

or it could just be that the file is write protected, to undo the write protection right click the file to "get info" and you can unlock it from there