Boyd’s Bible Dictionary:
(called together). The “congregation,” when called in a purely religious capacity (Ex. 12:16; Lev. 23:2; Num. 28:18).
Concise Bible Dictionary:
“A calling together,” and always called “holy.” The occasions called “holy convocations” are specially given in Leviticus 23 when the Feasts are recorded; they included the Sabbath, and ended with the Feast of Tabernacles. “These are the feasts of the Lord, which ye shall proclaim to be holy convocations, to offer an offering made by fire unto the Lord” (Lev. 23:37). It occurs also in Exodus 12:16; Numbers 28:18, 25-26; and Numbers 29:1,7,12. The same Hebrew word is translated “assemblies” in Isaiah 1:13 and Isaiah 4:5.