A cassette was a storage medium for audio or visual information.
A boy from Penge once gave Ace a cassette of Scoundrel Days, an A-ha album. (AUDIO: Project: Destiny)
Mortimus invented the CD a decade early to prevent the Seventh Doctor from hearing Plasticine's performance (which had originally been a bootleg cassette). (PROSE: No Future)
The Tenth Doctor stored the Wire on a Betamax cassette in 1953 and claimed that he was going to record over it. (TV: The Idiot's Lantern)
In 2600, Bernice Summerfield obtained two episodes of Blake's 7 on VHS cassette for Gavin Oliver Scott. (PROSE: The Least Important Man)