- the ratio of the radiant flux transmitted through and emerging from a body to the total flux incident on it: equivalent to one minus the absorptance.
- the act of transmitting
- a measure of the ability of anything to transmit radiation, equal to the ratio of the transmitted flux to the incident flux; the reciprocal of the opacity. For a plate of material the ratio of the flux leaving the entry surface to that reaching the exit surface is the internal transmittance
