The 2000 U.S. Census in the write-in response category had a code listing which standardizes the placement of various write-in responses for automatic placement within the framework of the U.S. Census's enumerated races. Whereas most responses can be distinguished as falling into one of the five enumerated races, there remains some write-in responses which fall into the "Mixture" heading which cannot be racially categorized. These include "Bi Racial, Combination, Everything, Many, Mixed, Multi National, Multiple, Several and Various".

What does the "mixture" heading mean?