A barrel with a full choke.
If you mean a choke bored barrel, it designates the amount of constriction a shotgun barrel has.
At the end of the barrel
choke of sears model 20 12 gage plain barrel shotgun has 3 stars on barrel
They came in various barrel lengths and choke combinations. If it is not marked on the side of the barrel, you will have to pattern the shotgun to determine the choke
A shotgun barrel with a cylinder bore choke.
The amount of constriction at the muzzle
It is possible
No. A choke tube slips into and screws to the muzzle end of the barrel. It can only decrease the inside diameter.
It has a nickel steel barrel and is a 12 gauge with a mod choke. It has a nickel steel barrel and is a 12 gauge with a mod choke. It has a nickel steel barrel and is a 12 gauge with a mod choke.
It is possible to fire a shotgun without a choke, but it is highly not reccomended, and they don't cost that much If you select a barrel with no choke (cylinder) it will cause the pattern to be looser than for a barrel of a shotgun that has a tighter choke. The extreme is "full choke" which keeps a tight pattern out to the effective range. Full choke is typically used for waterfowl. A shotgun that is pressed into double duty (shot for small game and slugs for big game) would work well to have modified choke. Slugs have to be designed to fire through a full choke without blowing the barrel but you will certainly shorten the life of the barrel by firing slugs through a choked barrel. If you can afford an extra barrel, then use a cylinder (no choke) for slugs. Remington and other shotgun manufacturers have interchangeable choke tubes (see link) that allow you to screw in the appropriate choke for your quarry.
the barrel is constricted at the end to make the pattern of shot flow density wider or tighter. Usually from cylinder up to full choke