Test summary report is a document which contains summary of test activities and final test results.
After the testing cycle it is very important that you communicate the test results and findings to the project stakeholders so that decisions can be made for the software release. i.e. If further testing is required and we need to delay the release.
Test Summary Report will be different for different kind of testing. Suppose you are doing risk based testing your report should contain the test coverage and unresolved defects against the product risks, and if you are doing requirements based testing then your test summary report should measure coverage against the requirements.
In addition to test coverage and unresolved defects test summary reports should also contain test strategy, test objectives and overall result of test effort.
IEEE 829 standard Test Summary Report Template
Test summary report identifier
Summary of results
Summary of activities