Engine light on! What is code P0171?

I have a 1999 Lexus RX 300. The engine light came on and the local auto shop plugged in and came up with this: “P0171 bank 1 system 2 lean” Any ideas? TIA!! Clay

Lean? Could it be the Slim Fast? ++ What is the BASIC cause of a lean engine or a lean cylinder? OK, I looked at the back of the book and got the answer: a lean condition exists when, during combustion, there is too much air, or too little fuel. Too much air could be from an intake manifold vacuum leak near that particular cylinder. Too little fuel could be from the fuel injector not spraying enough fuel.

consider addin sea foam to 8 gallion of gas or less and see if it cleans the system and corrects the problem…

I just googled the code and got over 39,000 hits.