Heuristic Evaluation
Heuristic evaluations are usually done early in the usability lifecycle. They can act as stepping stones to determine which usability issues to focus on during user testing or can be done by themselves.
The Clemson Usability Group will have 2 - 3 usability experts go step by step through your product. At each step the experts will determine if any usability heuristcs are being violated. Once violations are found, the expert will determine the severity of the violation as well as recommendations for improvements.
It is always recommended that the system should be tested by actual users, but a heuristic evaluation is a good starting point for testing or beneficial when changes to a system need to occur immediately.
Further reading
Clemson Usability Group