Every car sold in the European Union or in the United States is required to
have an on-board diagnostics (OBD) connector.
The OBD physical connector is standardized in SAE J1962.
The signal protocols are standardized in e.g. ISO 15765-4 and SAE J2284.
Diagnostic trouble codes (DTC) are standardized in ISO 15031-6 and SAE J2012.
Since standardization of OBD, it is commonly called OBD-2 or OBD-II.
Most popular OBD-2 adapters are based on the ELM327 microcontroller.
e.g. The Vgate iCar Pro Bluetooth adapter is based on ELM327 v2.3.