semi-casual是什么意思？

半正式的
就是介于休闲和商务之间的着装

介符正式与休闲的服装

半休闲的,介于休闲和商务之间的着装
semi-formal 半正式的

There is no such a thing as semi-casual.

We have formal dress and casual dress, and in between, we call it business casual.