Ada is Cardano’s native currency, which is named after Ada Lovelace, the English mathematician and programmer.
Ada can be used to pay transaction fees on the Cardano network and can also be delegated as stake to a stake pool, helping to secure the Cardano blockchain. Delegating ada allows the user to receive rewards for doing so. All rewards are distributed in ada every 5 days, i.e. every epoch.
Ada has six decimal places and these fractions of ada are called lovelaces. They can be thought of as cents to a dollar.