To celebrate a ceremony, you offer a congratulatory gift.

祝儀 generally refers to monetary gifts for celebrations, such as congratulatory money for weddings. It can also include money given away when you make a hole-in-one in golf or win big on a gamble.

While 祝儀 can also refer to the celebration itself, this use is not as common.

This is a jukugo word that uses the on'yomi readings of the kanji. The reading for 祝 is an alternate one that you haven't seen yet, so here's a mnemonic to help you remember it:

Your go-to congratulatory gift is a pair of shoes (しゅう). Most people just give money, but you'd rather give something practical, and nothing beats a nice pair of shoes. Congra-shoe-lations!