Reliability means the quality of being dependable and consistent. Something or someone reliable does what they're supposed to do, when they're supposed to do it, time after time.

A reliable car starts every morning, even in winter. A reliable friend shows up when they promise to meet you. A reliable student turns in homework on schedule. The word captures something essential: you can count on it.

Reliability matters because life requires trust. Scientists value reliable experiments that produce the same results when repeated. Engineers design reliable bridges that stay strong through decades of traffic and weather. Your parents need a reliable alarm clock to wake up for work. You need reliable information when researching a school project.

The opposite of reliable is unreliable or erratic. An unreliable bus that sometimes arrives on time but often runs late creates problems for everyone who depends on it. An unreliable narrator in a story might tell you things that turn out to be false or exaggerated.

Building reliability takes consistency and effort. When you prove yourself reliable by keeping promises and finishing what you start, people learn they can depend on you.