The definition of graceful degradation is designing something so that the system as a whole will work properly, even if an error occurs in execution. Graceful degredation is incorporated in both computer design as well as in mission critical or life-critical systems.
An example of graceful degradation is the process where emergency lights switch to the "on" position on a plane when the main power goes out.
An example of graceful degradation is the design of HTML webpage code that can display screen content regardless of the browser’s reduced functionality or lowered capabilities. For example, if the screen was written in code that was designed to be able to handle browsers of more limited functionality, at the point in the code that required the image to be displayed a text description of the image would be displayed and the rest of the page would then display as was intended.
A system that continues to run at some reduced level of performance after one of its components fails. It is a level below fault-tolerant systems, which continue running at the same rate of speed. For example, a two-computer complex employing graceful degradation would be reduced to using one system if the other fails. With fault tolerance, a third computer would be standing by to take over in the event of failure. See fault tolerant and graceful exit.