A few years ago I worked with a guy who regularly said “that’s my jam” in reference to his favourite music, and even his non-musical interests and activities. The jam he spoke of was likely an expansion of the musical jam, a noun that also became a verb. First recorded in 1929 as jazz lingo, it referred to a short improvised piece of music by a band.
One theory explains that 1920s musicians would often gather to play a different style of jazz, after their paid gigs with larger ensemble bands. When Bing Crosby attended these sessions he clapped on the first and third beat; described by the other musicians as jammin’ the beat.
A muso might be able to explain in what sense this jamming was intended. Perhaps “tightly packed” or “blocking”, but anyway, by 1933, the improvised jazz collaborations were known as jam sessions.
I favour a more bookish explanation (of course) from Etymonline.com:
The meaning of the kitchen jam (fruit preserve) dating back to the 1730s may have spread to the music scene with the suggestion of something sweet or excellent, giving us the jazz jam.
And the first recorded usage of jam to mean a treat or reward is from Lewis Carroll‘s Through the Looking-glass (1871):
‘I’m sure I’ll take you with pleasure!’ the Queen said. ‘Twopence a week, and jam every other day.’
Alice couldn’t help laughing, as she said, ‘I don’t want you to hire ME – and I don’t care for jam.’
‘It’s very good jam,’ said the Queen.
‘Well, I don’t want any TO-DAY, at any rate.’
‘You couldn’t have it if you DID want it,’ the Queen said. ‘The rule is, jam to-morrow and jam yesterday – but never jam to-day.’
‘It MUST come sometimes to “jam to-day,”‘ Alice objected.
‘No, it can’t,’ said the Queen. ‘It’s jam every OTHER day: to-day isn’t any OTHER day, you know.’
It didn’t take long before jam tomorrow became a popular phrase meaning the promise of something good, and by 1975 Hotten’s Slang Dictionary (5th ed.) had included:
real jam, a sporting phrase, meaning anything exceptionally good.
Fraser and Gibbons’ Soldier and sailor words and phrases (1925) gives us the first indication that our seafarers of the time were also floating it in their colloquial vocabulary.
PS The fruit preserve jam probably originated from a culinary use of the verb (to press or squeeze objects tightly) crushing fruit into a preserve.
The verb (1719) is thought to have been onomatopoeic from the sound objects can make when jammed together with force, akin to cham (bite, chew) or champ (to crush or chew noisily).
PPS If anyone knows anything at all about the Jemmy Squaretoes entry in this photo capture, I’d love to hear about it.