What is “Kwanza”?

I’m African, namely South African- Kenyan🇰🇪 🇿🇦. I recently made some American friends and they wished me a happy Kwanza. I have never heard of this holiday before.

For further context: kwanza - with one “a” is a word in Swahili - one of the languages I speak. So I apologise for the incorrect spelling. It means first/beginning.