party leaders' debate (in the Diet)
A formal debate held in the Japanese Diet between the leaders of political parties, typically the prime minister and opposition leaders.
In today's party leaders' debate, there was a heated discussion about economic policy.
The party leaders' debate is one of the important events in the Diet.
国会討論 is a broader term for any Diet debate, while 党首討論 specifically refers to the debate between party leaders.
Compound of 党首 (party leader) and 討論 (debate).