ROWS clause in the Query [Resolved]

The following example uses the ROWS clause to define a window over which the rows are computed as the current row and the N number of rows that follow (1 row in this example).

SELECT BusinessEntityID, TerritoryID 
    ,CONVERT(varchar(20),SalesYTD,1) AS  SalesYTD
    ,DATEPART(yy,ModifiedDate) AS SalesYear
    ,CONVERT(varchar(20),SUM(SalesYTD) OVER (PARTITION BY TerritoryID 
                                             ORDER BY DATEPART(yy,ModifiedDate) 
                                             ROWS BETWEEN CURRENT ROW AND 1 FOLLOWING ),1) AS CumulativeTotal
FROM Sales.SalesPerson
WHERE TerritoryID IS NULL OR TerritoryID < 5;

I didn't understand the use of/how the 'ROWS BETWEEN CURRENT ROW AND 1 FOLLOWING' will work in above query ? Pls explain

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Srihari [Resolved]