1.
club, circle (university/hobby group)
An informal group or club, especially at a university, organized around a shared interest or activity. Less formal and less competitive than a 部活 (official club).
2.
pen, enclosure (for a pet or baby)
A portable fenced enclosure for a pet or a small child (ベビーサークル, a playpen). For a circle as a plain shape, Japanese says 丸 or 円, not サークル.
Cultural note
In Japanese universities, サークル refers to casual student clubs, as opposed to 部活 (official athletic or cultural clubs), which are more structured, demanding, and competitive. サークル activities are more relaxed and social.
Usage
Sense 1 is the dominant meaning. Common question at university: どのサークルに入ってる？ (What circle are you in?)
Common collocations
- サークル活動: circle/club activities
- サークルの飲み会: circle drinking party
- 同人サークル: doujin circle (group producing fan works)