'leprecaun' is an imaginary little man from Irish legends.
He usually wears a little green hat and green clothes.
In March there is an Irish holiday, Saint Patrick's Day.
People usually wear green and drink beer on Saint Patrick's Day.
This blog is mainly to explain a different English language expression every day. Sometimes I post other stuff. I also have a YouTube channel which is mostly about computer software: https://www.youtube.com/englishspacedog