That is a signal that the onboard diagnostics system (or OBD II) has detected a malfunction in the vehicle’s emissions, ignition or fuel systems. It could be something as simple as a loose gas cap or something as severe as a faulty catalytic converter, so you shouldn’t ignore it. All cars and light trucks have onboard diagnostics that are supposed to detect engine-related problems that affect the emissions control systems.
The check-engine light (typically a yellow or orange outline of an engine with the word “Check”) should come on for a few seconds every time you start the engine with other warning lights. If it stays on, that means there is a problem.