This is the 718th most frequent German word.
circa
Approximately; about.
Here, 'circa' is used to indicate an approximation or estimate in measurement.
Die Strecke ist circa fünf Kilometer lang.
The distance is approximately five kilometers long.
In this context, 'circa' expresses an estimation regarding the number of students.
Circa 20 Studenten nahmen an der Vorlesung teil.
Approximately 20 students attended the lecture.
Here, 'circa' is indicating an estimated duration of the meeting.