noun, noun or participle which takes 'suru', intransitive verb
gregariousness; living in groups
Describes animals or people that naturally live in groups or crowds. Often used in biological or sociological contexts.
人間は群居する動物だ。
Humans are gregarious animals.
この鳥は群居性が強い。
This bird has a strong tendency to live in flocks.
群れる is a more common, everyday verb meaning 'to crowd together' or 'to flock', while 群居 is a formal, technical term for gregariousness as a trait.
社会性 refers to sociality or sociability in a broader sense, including complex social structures, whereas 群居 specifically emphasizes living in groups.
Compound of 群 (ぐん, 'group') and 居 (きょ, 'reside'). The exact historical derivation is uncertain, but the kanji composition directly reflects the meaning of living in groups.