The release of pent-up or repressed energies through their attachment to a new object or situation and their resultant release. For instance, the vicarious satisfaction of a desire to commit violence due to frustration with one's
boss, through something other than violence against one's
boss, e.g. through watching violent films, doing karate as a hobby, fighting a rival gang, playing
Doom, etc.
It's a concept
taken from Freudian psychoanalysis.
It also has a peculiar meaning in Gramscian
theory, where it refers to the rearticulation and reconfiguration of desires and passions into a new ideological/philosophical framework - roughly speaking, the achievement of a new, revolutionary formation of
desire.