Test summary report is a document which will contains summarized information about all the testing activities which include execution of test cases and final test cases execution results.
Its always important to have transparent communication about testing activities and status with stakeholders of software. Test summary report will help stake holders in deciding if software is ready for release to its end users or not. If software is not fit for release then more time for testing can be provided or proper expectation level will be set for end user.
Test summary document for different phase will be different. If risk based testing is performed or functional testing is performed then in that case test summary report should give information about the features that were tested or in terms of test coverage. Test summary should also contain information about know issues or unresolved bugs. Test summary report for requirement based testing then we need to provide information regarding testing coverage as per requirement.
Test summary should also contain test strategy, testing scope and testing objectives and constraints.