Refers to a group of sheep, often used in literal or figurative contexts.
丘の上に羊の群れが見える。
A flock of sheep can be seen on the hill.
羊の群れが牧草地を移動している。
The flock of sheep is moving across the pasture.
Compound of 羊 (ひつじ, 'sheep') + の (possessive particle) + 群れ (むれ, 'group, flock').