An executive summary slide is a single slide produced for business purposes that usually contains a brief statement of the problem covered in the business presentation.
In the case of a proposal presentation, this slide will contain a brief statement of the proposal in a single slide.
In an Executive Summary slide it is common to include background information, concise analysis and main conclusions, so the audience have the whole picture by looking just one slide.
The executive summary slide is often referred as management summary slide.
In the document version of an Executive Summary, it is common to include content between 5-10% of the length of the completed report, trying to wrap it in a one-page executive summary for a report that takes about 20 pages or less.
Similarly in a PowerPoint presentation, an Executive Summary slide for PowerPoint may be wrapped in a single slide (1 slide) summarizing a presentation of about 20 total slides.