A displaced emotion is one that is unconsciously redirected from the original object to a safer or more acceptable one. Displacement is one of the defense mechanisms that protect us from feelings or thoughts that are too painful or difficult for our conscious mind to deal with.
An example of a displaced emotion is when a wife, who is frustrated with her husband's lack of ambition, puts extreme pressure on her children to overachieve. Another example is when a teenager worried about his grades comes home and lashes out at his sister.
In both cases, the real object of the emotion is something that the person is unable to face, and so releases it towards a more convenient or safer object.