Choke is the constriction at the end of the barrel that regulates the circumference of the circular pattern produced by the shot as it leaves the muzzle. The the tighter the choke the smaller the pattern (theoretically and with in reasonable limitations). If i were you I'd get a 12 ga TDC barrel. I think it is about the most versatile barrel goin'you can change the chokes to fit you hunting or shooting situation and even get some sights that mount on the rib that when combined with MOD or IC choke make it a pretty decent slug gun. The sights are also good for turkey. Another option is the shorter turkey 24" barrel. I like a longer barrel for most shotgun hunting situations. As for shot size and choke for turkey, 4,5,or 6 for shot and full to xxx full for choke