Fluence
The physical dose quantity fluence (commonly denoted by the Greek letter Φ) indicates the flow per unit of area (A) of particles or otherwise. The name is derived from the Latijn word fluere, meaning "to flow". The corresponding unit is reciprocal square meter (m-2).The quantity fluence rate (dΦ/dt) is the flow per unit of area and per unit of time (t). The corresponding unit is m-2·s-1.
From the definitions it follows that fluence rate = flux density.