An abstract briefly summarizes each part of your research paper.  They are about a paragraph long and should be able to stand on their own.  A good abstract is accurate, self-contained, nonevaluative, and coherent. 

Abstracts are generally used:

• when submitting articles to journals, especially online journals
• when applying for research grants
• when writing a book proposal
• when completing the Ph.D. dissertation or M.A. thesis
• when writing a proposal for a conference paper
• when writing a proposal for a book chapter

There are two types of abstracts: Descriptive and Informative.

An executive summary provides an overview of the report. It:

• briefly covers all the main parts of the report (summary of research in the field, research methods, research results, discussion, recommendations, and conclusion)
• provides a concise statement of the findings and recommendations based on those findings
• appears on a separate page and is able to stand on its own
• is no more than one or two pages long
• is written for the non-expert audience who may not have the time to read the whole report