تعریف و معنای "(as) different as chalk and cheese"

What is the origin of the idiom "different as chalk and cheese" and when to use it?

The origin of the idiom "different as chalk and cheese" dates back to the notable contrast between two distinct substances: chalk and cheese. Chalk is a soft, white, powdery substance, while cheese is a solid, often yellow or orange, food product. The phrase is used figuratively to expresses a difference or dissimilarity between two things, emphasizing their contrasting nature.