A flock of ravens is group of ravens that have gathered together.
A “flock” is a bird flight formation where many birds fly in close proximity to each other, usually no more than 25 feet apart at the closest points. Flocks can come together spontaneously or they can be man-made by people like the huntsman who may create large flocks for hunting. The term “assembly”, which should not be confused with the word assembly as to propose a law, describes when smaller groups join into one large group and end up making one pile from all their joining bodies and minds. This is what my paragraph below about the two functions of a flock: One function as an assembly point away form predation risk (like under a rock overhang or in a thicket of bushes) and the other function is to roost where they sleep at night.