It means that you can buy advertising space on LinkedIn based on an auction and you pay whatever price an ad is worth at a given moment. It saves you a lot of time as a machine handles a lot of the media buying processes for you and helps you buy specific audiences using lots of data to figure out the right ad, the right person, the right time.  

LinkedIn is by far the most scaled platform for business professionals out there and you can reach a lot of them in a highly targeted way.