The "K" is to identify that it is an airport located in the United States.
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This type of identification signifies what airport this is and where that airport is located. The FAA LID 40G airport identifier refers to Valle Airport in Valle, Arizona.
PIK
That is the airport's IATA Code identifier.
HXD is the airport identifier. (Or KHXD depending what you are using it for.)
A location identifier is the aviation "name" of an airport. For example, Cleveland, Ohio is CLE. When a pilot files a flight plan, he uses identifiers and route numbers of the airways he intends to fly, ending with the destination airport identifier.
It is often referred to as MBJ. The official ICAO identifier is MKJS.
The airport code for Gordon K. Bush Airport is ATO.
The airport code for W. K. Kellogg Regional Airport is BTL.
The airport code for Merle K. - Mudhole - Smith Airport is CDV.
According to Drugs.com's Pill Identifier, a round white tablet imprinted with 'K 18' is Oxycodone 5mg.
W. K. Kellogg Regional Airport was created in 1943.