What is the meaning of "rolling" here?

meaning-in-context meaning

To put it in layman's terms, as it is updated with more more current data, an equal time period "rolls off" the report.

For example, in a 12-month rolling report, the column or report for January 2020 would have information for Feb 2019 - Jan 2020. The column for Feb 2020 would have Mar 2019 - Feb 2020

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