Learning the theory of Langlands correspondence, I met the notion of "special" maximal compact subgroup of a (reductive) algebraic group over a local field.

Here, I think the word "compact" is used in analytic meaning.

The textbook I used did not explain the definition of "special".

My questions:

(1) What is the definition of "special" maximal compact subgroup?

(2) Is there any concrete example of maximal compact subgroup which is NOT "special"?

Please give me any advice.