also: せいかく
noun
General term for the most important guest at a gathering, event, or formal occasion.
今日のパーティーの正客は社長です。
The guest of honor at today's party is the company president.
noun
main guest at a tea ceremony
Specifically the principal guest at a Japanese tea ceremony (茶道).
茶会では正客が最初にお茶をいただきます。
At a tea gathering, the main guest receives tea first.
主賓 is a more common and general term for 'guest of honor' at formal events, while 正客 is often associated with traditional or tea ceremony contexts.
Compound of 正 (proper, main) and 客 (guest). The reading しょうきゃく uses the on'yomi of both characters, while せいかく is an alternative on'yomi reading.