To maintain something means to keep it in good condition or to continue it over time. When you maintain your bicycle, you oil the chain, check the tires, and make sure everything works properly so it doesn't break down. When a city maintains its roads, workers fix potholes and repaint lane markers. When a gardener maintains a lawn, they mow, water, and pull weeds regularly.

Maintain also means to keep something going or to preserve a state of being. A runner might maintain her speed throughout a race, keeping the same pace from start to finish. A student who maintains good grades doesn't let them slip as the year goes on. When you maintain a friendship, you stay in touch and keep the relationship strong over time.

The word suggests steady, ongoing effort rather than one big action. You don't maintain something once and forget about it. A museum maintains its collections through constant, careful work: controlling temperature, preventing damage, and making small repairs. That's very different from restoring something that's already fallen apart, which requires much more work.

People also use maintain to mean firmly stating that something is true: “She maintained her innocence” means she kept insisting she didn't do it, even when others doubted her.