What is it?
It was popular from 1965 to the 70s. Consisted of endless loop of 1/4 inch magnetic tape, which had 8 parallel soundtracks. Often associated with listening in a car, even though it was first developed by an aircraft manufacturer. It had a recording length of up to 80 minutes. It was eventually abandoned in favour of the cassette.
Who used it?
People used it in their cars and their homes. At its height, it was the most popular of tape systems and had the biggest music library available. It was the first mass produced car music format.
What was it for?
Developed for music systems in cars. (An older version, 4 track tape, were marketed as CARtridges lol). Car manufacturers in the 60s would give away a free 8-track if you bought a car with an 8-track player!
What craft was involved?
Multi-track recording, which was first developed in the 1950s. It allowed for superior recording, especially of music, because it meant that every sound, e.g. vocals or guitar, could be recorded on a different track, and thus allowed the studio engineers to edit each track differently.
Sources:
https://en.wikipedia.org/wiki/8-track_tape
http://www.recording-history.org/HTML/8track1.php
http://www.collectorsweekly.com/articles/god-save-the-eight-track/