An executive summary is a stand-alone document, or part of a larger report, that serves to introduce a business plan, position paper, or investment proposal to a specific audience. This may include potential investors, partners, project directors, or upper management. The purpose of the executive summary is to entice the audience into reading the whole report, where they will find details such as data, projections, earnings reports, tables, and analysis. 

The executive summary is not a place for wit or verbosity. The length is typically short, between one and three single-spaced pages, and the tone should be concise. That said, executive summaries can run the risk of oversimplification, reducing complex ideas to short, easily digestible bites that erase nuances. With the limited space allowed, writers should be careful to make sure that the executive summary provides only an overview of and context to the contents of the full report.

Introduction

• The voice should be compelling but not clichéd.

• Define the problem, issue, or pitch.

• Define the purpose of the larger report quickly and succinctly.

Body

• Focus on creating clear, concise language.
• Summarize what is included in the report as a narrative.
• Match the narrative to the goals of the audience.
• Think about relationships.
• How is the situation unique?
• What specifics need to be included to draw the audience’s attention?
• Might there be an advantage in a particular market?

Conclusion

• Remember: The mission is to have the audience interested in reading the full report.
• The executive summary can also be a stand-alone document, so it needs to come to a clear conclusion that invites the reader into the remainder of the document.

Reference

https://www.inc.com/guides/2010/09/how-to-write-an-executive-summary.html