Reliability is the core underpinning of a good software system. Without reliability, the usefulness of technology quickly dissipates, leaving us in a position where we may have been better going without it. Technology's entire purpose can be undermined by unreliability.

Reliability, however, is not only a characteristic of large and complex software systems. Each and every line of code can be constructed to be either unreliable or reliable. But what do we mean by this? Reliability, the word, refers to the quality of being reliable. What does it mean to write code that people can rely on? It helps by defining reliability in terms of three distinct qualities: Reliability is the quality of being correct, stable, and resilient.