The word "whatever" is used to indicate that you are indifferent or do not have a strong preference for something. It can mean "anything" or "everything" in a nonchalant way, suggesting that the specifics are not important. "Whatever" can also imply acceptance of any option or choice presented.
The word "whatever" comes from the combination of "what" and "ever." It has been in use since the late 14th century, originally meaning "whatever one chooses," and has evolved into a term used for expressing indifference.