How much the shot is constricted as it leaves the barrel.
Unknown.
Improved cylinder
# They relate to choke type, i.e., full, modified....
If you mean a choke bored barrel, it designates the amount of constriction a shotgun barrel has.
4 notches = cylinder choke (open), and one notch = full choke (tight)
They probably denote what choke the barrel has.
It stands for Modified choke.
Degree of choke
Go here for a good explanation - http://hunting.about.com/od/shotgun/l/aastshotgunfaqa.htm
yes it is a choke marking. What you list doesn't follow the normal convention.
Remington tactical choke refers to a type of shotgun choke tube designed for tactical or defensive shooting scenarios. These chokes are engineered to provide a specific shot pattern and improved performance with various ammunition types, often enhancing accuracy and effectiveness in close-range situations. They are typically used with Remington shotguns and are preferred by law enforcement and military personnel for their reliability and versatility in dynamic environments.