2 3 4 8 A B C D E F G H I J K L M O P R S T U V W
Sc Sd Se Sf Sh Si Sl So Sp St Su
Sec Sen Seq Set

Second Second Assistant Director (2nd 2nd AD)

Yes, this is a job title! This individual supports the 2nd AD and handles background extras and crowds. Sometimes, if there are big enough crowd scenes, there will be several 2nd 2nd ADs on a set.