Rolling returns, also known as "rolling period returns" or "rolling time periods," are annualised average returns for a period, ending with the listed year. Rolling returns are more robust than trailing returns. 3Y rolling returns would involve going back 3 years and then calculating the past 3 year returns every day since then and then averaging those numbers.
Rolling returns in comparison to trailing returns are more likely to be an expected achievable return from the investment in the future.