NASCAR Racing: free pass, wrecked cars, flag stand

Question
I just started watching nascar and I would like to know what this free pass is and how it works

Answer
As of a couple years ago the drivers were allowed to "race back to the yellow flag", meaning they could try to pass as many cars as they could until they got back to the flag stand where they would get the yellow flag. This made for danger to the wrecked cars and many cars making a "mad dash" to get past the leader to get a lap back. In order to improve safety NASCAR now "freezes the field" when the yellow comes out, not allowing any more passing. In order to allow lapped cars to still have a chance to get past the leader and get a lap back they now allow the first lapped car to get a "free pass" and get his lap back. Kind of a "we took away your chance to get a lap back by driving crazy and gave one of you a safe chance to get that lap back".