Had a smog test and a PO172 trouble code -System too rich (bank 1) what is this?

 

It means the bank of cylinders that incorporates cylinder #1 is running rich.
Air filter could be dirty/plugged, vacuum hoses could be leaking, leak at intake manifold gaskets, too much fuel/too high of fuel pressure being injected into the engine, weak ignition system. In dire need of a basic tuneup...

But it would be helpful if it was known what make/model/sub-model/year/drivetrain/etc