noun
A Buddhist ceremony held to commemorate the deceased, typically on specific anniversaries after death.
来週、祖母の三回忌の法要を行います。
Next week we will hold a Buddhist memorial service for my grandmother's second anniversary of death.
法事 is a more general term for Buddhist memorial rites, while 法要 specifically refers to the formal ceremony itself.
From 法 (Buddhist law/teaching) and 要 (essential point), referring to the essential Buddhist rites for the deceased.