The purpose of an executive summary is to provide a concise and accurate summary of a larger document, or multiple documents, for an executive who most likely does not have the time to read the original report. It needs to give a recommendation based on the key findings of the report.
Think of an executive summary as a cover letter for your report.
Executive Summaries are much like any other summary in that their main goal is to provide a condensed version of the content of a longer report.