No, maybe I'm reading your quote wrong.Is this a trick question?
A rolling period includes two or more continuous years and all such periods over the time frame selected. As an example, over any given 10 years, there are eight 3-year rolling periods (1986–1988, 1987–1989, 1988–1990, 1989–1991, etc.). The advantage of using rolling periods is bad returns cannot be hidden as easily.