noun
first trading session of the year
Refers specifically to the opening day of trading on Japanese stock exchanges after the New Year holiday. Often involves a ceremony.
東京証券取引所の大発会は1月4日に行われた。
The Tokyo Stock Exchange's first trading session of the year was held on January 4th.
大納会 is the last trading session of the year, while 大発会 is the first session of the new year.
Compound of 大 (dai, 'big') + 発会 (hakkai, 'opening of a meeting or market'). The term is specific to Japanese stock exchange culture.