According to the Webster dictionary, Listening, a verb, means to give one’s attention to a sound: “sit and listen to the radio”. Take notice of and act on what someone says; respond to advice or a request: “I told her over and over, but she wouldn’t listen”.
Where as, monitoring, Verb, to Observe and check the progress or quality of (something) over a period of time; keep under systematic review. Maintain regular surveillance over: “it was easy for the enemy to monitor his movements”.
So it looks like listening is active and monitoring is passive. In marketing, listening is paying attention to what customers are doing and acting upon it. – EJB