And freeform jazz is mostly best consumed on a large sofa with a few bottle of red and the lights off, imo.

I was going to say some elements of Tony's explanation but only knew that there was an underlying rythm that everybody just plays what they want to... kinda like 'Jamming'

Can is a good example of freeform music. They just recorded months of stuff in their studio at Inner Space then edited the best bits into albums. Live versions just took key themes then just worked together to go on an unknown journey. I recommend anybody to get a copy of Cannibalism vol 1 and vol 2.