what is a forbidden riff

The term "forbidden riff" refers to any overplayed song that has been jokingly banned from being played in guitar stores. These are typically well-known, but easy-to-learn riffs and licks that guitar store employees are fed up of hearing on a daily basis, such as Stairway to Heaven. These tracks are particularly frustrating to guitar stores as almost every new guitarist learns these forbidden riffs, and almost every new guitarist thinks they are the only one to ever learn them. The term "forbidden riff" is mainly just an inside joke within guitar culture, and the whole idea of a forbidden riff is mostly a joke among guitarists today.