Usually, you run tests according to a test plan. If needed, you can also run test suites.
A test plan can have test suites from several applications. A test suite can have test cases from but one application.
Each time you run a test, a test run is created. All elements of the test plan or test suite that you run are added to the test run.
Example
You run a test plan. As a result:
Each of its test suites is run.
For each of these test suites, also the defined test cases are run.
For each of these test cases, also the defined test scenarios are run.