What are usability heuristics? List and explain three usability heuristics.

Usability heuristics are broad rules of thumb that serve as a guide for user interface design. They are not specific usability guidelines but rather provide a general framework to evaluate the user interface. Here are three usability heuristics:

1. Visibility of System Status: This heuristic emphasizes that the system should always keep users informed about what is going on, through appropriate feedback within a reasonable time. For example, if a user is filling out a form online, the system should inform the user about the successful submission of the form or any errors that occurred during the process.

2. Match between System and the Real World: The system should speak the users' language, with words, phrases, and concepts familiar to the user, rather than system-oriented terms. It should follow real-world conventions, making information appear in a natural and logical order. For example, an e-commerce website should use terms like "Cart", "Checkout", "Payment" which are commonly used and understood by users.

3. User Control and Freedom: Users often choose system functions by mistake and will need a clearly marked "emergency exit" to leave the unwanted state without having to go through an extended dialogue. The system should support undo and redo functionality. For example, if a user accidentally deletes an email, they should be able to retrieve it from the trash or undo the delete action.