noun
first meeting; initial gathering
Refers to the very first meeting or assembly of a group, committee, or organization. Often used in formal or organizational contexts.
新委員会の初会合は来週の月曜日です。
The first meeting of the new committee is next Monday.
両国の首脳による初会合が実現した。
The first meeting between the leaders of the two countries took place.
第一回会合 explicitly means 'the first meeting' in a numbered series, whereas 初会合 simply means the initial meeting without necessarily implying a series.
Compound of 初 (hatsu, 'first') + 会合 (kaigō, 'meeting, assembly').