Test run

ISTQB Glossary  definition 

"Execution of a test on a specific version of the test object."

In Simple English,

Every attempt you make to formally execute the steps of a test case is a test run.

Field Notes 

• Test runs are formally tracked in test management tools most times
• Test runs are applicable only to certain formal testing methods and not all.
• Test methods like exploratory testing do not have a formal test run.

For Example:

Say, you are trying to test a login page.

One test case would be to to give a incorrect password and expect an error message which says "Error: In correct password entered.".

Now when you first test this page it say it says another error message "Error: User does not exist". You now have completed one test run and have observed an deviation from expected result.You would log this as an defect. Now you have just completed one test run.

Now after logging the defect you want to see if the defect is repeatable. You perform the steps of the test case one more time and see that the same defect occurs. Now you completed the second test run for this same test case.