Also, what
musicians do when they get together. I'm thinking about those that can loosely be called popular musicians.
When my band, Missing Neutrinos, came over to my place on Sunday afternoons we would jam our blues, many of which I've noded (see the Unattributed Blues Metanode).
I suppose the derivation is jamming musicians together, causing "an injury caused by jamming".
But what an injury!
There is little that compares with playing changes that are just easy enough to work from memory, but just hard enough so little accidents happen. You use everything you have, but it seems like magic--suddenly new, really cool stuff happens.