at the conference—
1. in the course of the conference:
- A good deal of discussion at the conference has been about pluralism.
2. attending the conference:
- The gays at the conference were all people who had “come out”—that is, openly declared themselves to be homosexual.
in conference—busy at a meeting to discuss smth. or exchange views:
- He went to see the managing editor, but Percy was in conference with the publisher.