It doesn't make for terribly interesting reading, unless you're a sailor, but is a breakdown of... well, what the title says. The COLREG
s have rules for lights, shapes, and specific pennants to be shown at various times, so if you're wondering why there's a reference to a certain light setup/shape doodled in your logbook/pennants flown for reasons you don't understand. You can look it up here.
This could probably be better served in the Outside Links topic, but that's locked :p