Term used in The Matrix to describe the virtual representation, within the matrix, of each human being that is plugged into the system.

Morpheus describes it as "the mental projection of one's digital self".

The residual self image is fully interactive with the rest of the matrix system. It carries out all the actions as directed by the mind of the human being plugged in to the system. The person is completely immersed within the matrix, and all senses felt by the brain through the RSI overrides those received from the real body.

It can be theorized that one who has mastery over the matrix will be able to manipulate their own RSI. This is only a theory as it has not been demonstrated so far in The Matrix trilogy.

BTW, The Matrix is an awsome movie. But that's only a personal opinion. The node for The Matrix has some awsome writeups. Read them if you haven't already.