What is "eavesdropping"?
According to Cambridge Learner's Online Dictionary to eavesdrop: is to secretly listen to a conversation. (E.g. "He stood outside the door eavesdropping on their conversation")
In most societies this is a considered impolite ( to behave in a way that is not socially acceptable) and many people will get angry if they find someone else doing it.
However, as a second language learner it is vital to eavesdrop on others in order to increase your listening ability, comprehension, and even to learn more words.
When you are living in a country where your target language (the language you are learning) is spoken don't listen to your mp3 player on the streets or on the train. Turn it off. Listen to the conversations around you,but try not to make it too obvious (easy to see or understand)!
Eavesdropping is bad manners, but as a second-language learner I think it is an essential skill. Just don't use your powers for evil, ok?