KK Definition

abbreviation
(Internet slang) Okay okay; indicates that no further explanation is necessary for a subject, or that the message was understood and will be acted upon without further confirmation.
Wiktionary
(Internet slang) Okay cool; a shortened response usually used at the end of a conversation.
Wiktionary

(aviation, travel) Confirm. (Originally a GDS status code, now often used as shorthand).

Wiktionary
symbol

(metrology) Symbol for the kilokelvin, an SI unit of thermodynamic temperature equal to 103 kelvins.

Wiktionary