济济一堂 [- - yì tánɡ]a gathering of many people; (A big audience) filled the hall.; a great assemblage of people in a hall; a large gathering in an auditorium; gather together under the same roof; The house is packed with guests.:
•¶ 老、中、青济济一堂， 共同学习， 相互激励。 Gathered together, the old, the middle-aged and the young studied side by side and encouraged each other.