What is VH/VW (viewport height/ viewport width) in CSS?

VH and VW are CSS units used to measure viewport height and viewport width respectively in percentage form in the responsive design techniques. E.g. If the height of the browser is 1000px, then VH is 1/100 of the height of the viewport that is 1000px*(1/100) = 10px, which is the height of the browser.  The same applies to VW (viewport width).