Dim sum - small dishes of food normally served at a Cantonese lunch.  It is a generic name that refers to a type of food.  The genre includes dumplings, but there are non-dumpling dim sum, such as spring rolls, barbecue pork buns, Cantonese sponge cake, Chinese cannelloni, etc.

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Aha i understand the analogy now.

No, you misunderstood.  That was meant to be an analogy to explain the logic of a "set and its relationship with its subsets", or "a category and its constituents".

What do you mean by the "Children are human beings, but not all human beings are children."?

I just mentioned my experience. Is a man considered childish if the person got wrong information or confused by a person?