Corner worker-- a track offical positioned generally before a corner to provide flag communication to the drivers and radio communication to the track steward. It is absolutely critical that you know where they are, and look at each one on each lap of your driving session. The corner worker may provide information that will save both you and your car from serious harm due to unsafe track conditions ahead. They'll also be the ones to let you know a faster car is approaching you, and whether something is wrong with your car that you are not aware of. Pay close attention to these people -- they're there to protect your life.