To depend on something means to rely on it or need it to happen. When you depend on your alarm clock to wake you up for school, you're counting on it to work. When a plant depends on sunlight, it needs that light to grow and stay alive.

The word often appears with “on” or “upon”: you depend on your friends to keep secrets, or a successful camping trip depends on good weather. Sometimes things are dependent: a baby is completely dependent on adults for food and care.

You can also say something depends when the answer isn't simple. If someone asks whether you can come to their party, you might say “it depends” because your answer relies on other factors, like whether you finish your homework or whether your parents say yes. A coach might tell the team that playing time depends on effort at practice.

When something is dependable, you can count on it consistently. A dependable friend shows up when they promise to. A dependable car starts every morning.