What is a 'pending' diagnostic trouble code and what does it mean?

A pending code is a fault that has been detected on one trip but has not yet been confirmed on a second consecutive trip, so the Check Engine light has not been turned on yet. It is identified on the Code Reader's LCD display by a numeric code accompanied by the word 'PENDING,' and the YELLOW LED will be lit. If the same fault is detected on the second trip, the code becomes a confirmed DTC and the Malfunction Indicator Lamp (MIL) will illuminate. (Page 19)