Efferent codes or nerve fibers are outgoing or axonal projections which exit a region. Generally these are going to other parts of the brain, or they are going to the periphery (i.e. extremities). These are the opposite of Afferent Codes.
Afferent codes (or afferent nerve fibers) are information (or axons) which carry information from the periphery (i.e. the extremities) to the central nervous system. These flow in the opposite direction of Efferent Codes.
Efferent Codes the actions (act, react, behavior…)