Boyd’s Bible Dictionary:

(place). The place in the temple where gifts were received (1 Chron. 9:26; Mark 12:41; Luke 21:1; John 8:20).

Concise Bible Dictionary:

A part of the temple was called “the treasury,” in which were kept things consecrated to Jehovah, as the gold, silver, and vessels of brass and iron captured from Jericho (Josh. 6:19). The free-will offerings of the people were also given in at “the treasury” (Mark 12:41,43). On one occasion the Lord spoke to the people “in the treasury, as He taught in the temple,” doubtless in the outer part where He could watch the people bringing in their gifts (Luke 21:1; John 8:20).