Commodore data cassette
The Commodore data cassette format was used to store programs and data on cassette tapes from Commodore computers (PET, C-64, etc.). It was so notoriously slow that even the rather sluggish Commodore 1541 disk format was lightning-fast in comparison. Most commercial Commodore cassettes ended up using "turbo loaders" which were stored first on the cassette in standard Commodore format, then executed to install a new load command which used shorter pulses, a format in which the actual program was stored.
Tap files are a format for storing the raw pulses of a Commodore cassette in a file suitable for storage and transfer in modern computer systems and networks.