> I can't find "jam" in any poker slang dictionary.
Jam: a preserve with bread and tea. ;)
Seriously, the best place to look up poker terms is Michael Wiesenberg's epic tome, The Official Dictionary of Poker. Available at fine bookstores, online outlets, etc. ALSO available for free on the web, but don't tell him I told you. [1]
http://www.planetpoker.com/games/dictionary/vocabj.asp#15734
Other web-based resources are available, as well:
http://www.rgpfaq.com/glossaries.html
And, yes, it means to put all of one's chips in the pot.
[1] Actually, I think he subscribes to this list, which allows me to finally ask the question that's been bugging me for weeks: is he a little peeved that his name is misspelled in Holden's "Big Deal?" -- https://stubing.kerndt.com/mailman/listinfo/ba-poker