noun, noun or participle which takes 'suru'
thriving business; prosperous trade
A yojijukugo used to describe a business that is doing very well, often as a wish or greeting. Can be used as a noun or with する to mean 'to prosper'.
今年も商売繁盛を祈っています。
I pray for your business to thrive again this year.
あの店はいつもお客さんでいっぱいで、まさに商売繁盛だ。
That shop is always full of customers; it's truly a thriving business.