Heuristic Evaluation is a process of accessing product’s usability and accessibility based on 10 heuristic principles defined by Jakob Nielsen:

• Visibility of system status
• Match between system and the real world
• User control and freedom
• Consistency and standards
• Error prevention
• Recognition rather than recall
• Flexibility and efficiency of use
• Aesthetic and minimalist design
• Help users recognize, diagnose, and recover from errors
• Help and documentation

Heuristic evaluation is typically carried out by a qualified UX or Interaction Designer. While it allows to uncover a number of usability and accessibility problems in the system, it is by no means a substitute for user testing.