An abbreviation of シンポジウム. It refers to a symposium or panel-style academic/public discussion event; the full シンポジウム is a little more formal and explicit.
See also: シンポジウム
They held a symposium at the university.
A symposium on environmental issues will be held at the university next month.
I attended an international symposium.
I took part in the symposium on my professor's recommendation.
He presented his research findings at the international symposium.