What is a test case?

A test case is a procedure defined to verify that the program works correctly without any unexpected issues.

A test case is composed of test steps that describe what actions should be done by the manual tester. Each step can have assigned a definition of expected result.

When the tester does the testing following the test case, we are saying he is executing a test case run. Within the test case run, he follows the test case step by step. After he finishes each step, he compares the actual result against expected result and marks the test step either as passed or as failed.

Multiple test cases can be defined for testing specific functionality. The test cases can be organized into a test suite.