since it's apparently a media creation according to some of you, here's the explanation from wikipedia:
In the United States, a White Hispanic or White Latino is a citizen or resident who is racially white and of Hispanic descent. White American, itself an official U.S. racial category, refers to people "having origins in any of the original peoples of Europe, the Middle East, or North Africa" who reside in the United States.
Based on the definitions created by the Office of Management and Budget and the U.S. Census Bureau, the concepts of race and ethnicity are mutually independent, and respondents to the census and other Census Bureau surveys are asked to answer both questions. Hispanicity is independent of race, and constitutes an ethnicity category, as opposed to a racial category, the only one of which that is officially collated by the U.S. Census Bureau. For the Census Bureau, Ethnicity distinguishes between those who report ancestral origins in Spain or Hispanic America (Hispanic and Latino Americans), and those who do not (Non-Hispanic Americans). The U.S. Census Bureau asks each resident to report the "race or races with which they most closely identify."
White Americans are therefore divided between "White Hispanic" and "Non Hispanic White," the former consisting of White Americans who report Hispanophone ancestry (Spain and Hispanic Latin America), and the latter consisting of White Americans who do not report Hispanophone ancestry.