Check Engine Light. A self test that the bulb is good, if it remains after engine is running, codes need to be read.

If your car was made in 1996, or thereafter, attach a code reader to the data link connector, located under the dash, if the CEL stays on. It will read any codes stored in the ECM.

CEL: Check Engine Light
MIL: Malfunction Indicator Lamp
SES: Service Engine Soon Light
etc...
Different manufacturer's use different acronyms and names for the same thing. The whole idea is to alert you if something is causing your engine to create excessive emission, generally 1.5 times the Federal Test Procedure (FTP) standards, which vary from model to model and year to year.