OBD stands for “on-board diagnostics” and if you own a car that’s from 1996 to today, beneath the driver’s side dash there’s a little plug/port that resembles the port you’d plug your desktop computer’s monitor into on the tower. This is your car’s OBD2 port and is designed to help automotive technicians to diagnose faults and other issues your car may have by recording codes that mean various things.
An OBD2 scanner is a small electronic device that plugs into your car’s OBD2 port that reads those codes. As mentioned above, this was once the tool of professional mechanics and dealerships. However, as with all technology, it became cheaper and cheaper to manufacture and the public’s desire to work on their own vehicles made them become consumer tools.