A meeting of a religious character as distinguished from congregation, which was more general, dealing with political and legal matters. Hence it is called an "holy convocation." Such convocations were the Sabbaths (Leviticus 23:2,3), the Passover (Exodus 12:16; Leviticus 23:7,8; Numbers 28:25), Pentecost (Leviticus 23:21), the feast of Trumpets (Leviticus 23:24; Numbers 29:1), the feast of Weeks (Numbers 28:26), and the feast of Tabernacles (Leviticus 23:35,36). The great fast, the annual day of atonement, was "the holy convocation" (Leviticus 23:27; Numbers 29:7).
These dictionary topics are from M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition, published by Thomas Nelson, 1897. Public Domain, copy freely.
Easton, Matthew George. "Entry for 'Convocation'". "Easton's Bible Dictionary".