CTD.

Super-Full And Extra-Full Chokes

Known as gobbler getters, these are ideally suited for the headshots necessary in turkey hunting. They have extra-tight constrictions and the densest patterns.

Full Choke

A full choke has tight constriction and a dense pattern, delivering approximately 70 percent of a shell’s total pellets in a 30″ circle at 40 yards. It’s best for trap shooting, waterfowl pass shooting, turkey hunting, and buckshot loads.

Modified Choke

The modified is characterized by less constriction than full choke, delivering approximately 60 percent of a shell’s total pellets in a 30″ circle at 40 yards. Excellent for all-around hunting of waterfowl, long-range flushing of upland birds (such as late-season pheasant and sharptail grouse) as well as other small game. It’s also used for trap shooting.

Improved Cylinder Choke

Even less constricted than modified, the improved cylinder distributes approximately 50 percent of a shell’s total pellets in a 30″ circle at 40 yards. Ideal for close-in small-game shooting, upland bird hunting (such as quail, grouse, and pheasant) as well as hunting waterfowl close over decoys. Rifled slugs also perform very well with this choke.

Cylinder Bore

A cylinder bore provides no constriction and distributes approximately 40 percent of a shell’s total pellets in a 30″ circle at 40 yards. It’s most often used by law enforcement for service shotguns.

Skeet Choke

A skeet choke is a specialty choke that sends approximately 50 percent of a shell’s total pellets in a 30″ circle at 25 yards. This type is designed to deliver optimum patterns for close-range skeet shooting.

I found this informative as a good summary, but one of the best things I learned was in the comments.  I confess I didn’t know this.

Q: Is it safe to shoot 12 gauge slug on the Benelli M4 with a modified choke?

A1: It is not recommended to shoot slugs through a modified choke. Cylinder and Improved Cylinder are acceptable for rifled slugs, as they have the least constriction. Additionally, you can purchase a rifled choke, which will allow you to shoot sabot slugs (at what level of accuracy, I am not sure).

A2: Not only can shooting a slug through a full choke be potentially hazardous to the barrel (and in very extreme cases the shooter), accuracy will typically be poor since the slug is heavily compressed as it passes through the choke. I typically recommend cylinder bore or improved cylinder for shooting rifled slugs, though I know some old timers that swore by their modified chokes for slug shooting.

If some shotgunners would like to add to this, do so in the comments.