sad occasion; funeral
Refers to a mournful event, especially a funeral. Often used in contrast with 祝儀 (しゅうぎ, 'happy occasion').
At a funeral, you should avoid flashy clothing.
There are noshi envelopes that can be used for both happy and sad occasions.
祝儀 is money given at a happy occasion like a wedding, while 不祝儀 is money given as a condolence offering at a funeral.
Compound of 不 (ぶ, 'not') and 祝儀 (しゅうぎ, 'celebration'), literally meaning 'non-celebration'.