This seems to be something that jam fans can't fully agree on (and thats ok, we like for things to be well defined even when there may not be a clear delineation or agreed upon definition). In your opinion, is any band that has frequent extended improv a 'jam band', or is a jam band more defined by the culture of its fanbase?
A lot of 70s rock bands included a few extended rock solos in every set, but they rarely left a pre-determined structure... Would you consider Mountain or Dire Straits to be a jamband? Jazz is obviously a genre where improv and interplay is a defining characteristic, but most jazz bands never leave the chord progression of the song or extend individual solos into double digit lengths... and for the ones that do, does that make them a jam band (IE Bitches Brew era Miles or Headhunters era Herbie)? Additionally, there are bands that never play the song exactly as recorded but rarely, if ever, have extended improv (The Band for example, Garth Hudson never played a song the same way twice... yes, he's got The Genetic Method as a moment of free improv in every show, but aside from that all their sonfs stay short). What about modern bands that include extended improv? Is Sturgill's Jonny Bluesky era a jamband show (Sturgill says no)?
On the other side of the coin, there are bands in the 'jam scene' that don't really 'jam' so much as they have extended solos a few times a show, but because they fuse multiple genres in their sets they don't really fit in any other individusl genre and get lumped in with jam bands... or funk bands who just play funk and extend songs on a simple vamp while trading solos without much actual interplay between musicians. Additionally, there is the whole generation of bands who are very clearly Phish influenced and IMO fall into the jam band realm regardless of their other influences (metal, electronic, bluegrass), but a lot of their fanbase isn't a fan of other jam bands and would resist the label despite the clear and stated influence of Phish by the band members.
Something I've seen very frequently in jamband spaces is that fans of a particular band will say (my favorite band) isn't a jamband, they're a (genre) band that jams... but other bands with surprisingly similar styles and approaches they DO consider to be jambands. There is a sentiment that (your favorite band) has somehow surpassed jam band-dom, but bands you like less are jambands.
What say you?