Does anyone know the exact definitions of these conditions using the “Group By” function on the front end of looker?

Does anyone know the exact definitions of these conditions using the “Group By” function on the front end of looker?
I am curious the different between “is” and “contains.” Is there a field where a category can contain 1 item including another. I noticed when using the group by function it automatically says “OR” instead of and. For example…
However I noticed that the second bullet, when using the contains function, it automatically says jacket OR pants.
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