Crowd, Multitude
noun, verbal noun
A flock that has gathered is a crowd and multitude. Because, well, lots of things gathering.
ぐんしゅう
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
小さな男の子がジャスティン・ビーバーの物真似をし出したので、群集は大笑いをしました。
The crowd broke out in laughter when the little boy started imitating Justin Bieber.