Groundwater flow velocity (specific discharge) is defined as a new version of conventional Darcy law by considering dynamic transmissivity concept which is equivalent to the multiplication of piezometric head and hydraulic conductivity. Hence, the groundwater velocity is expressed as a non-linear spatial variation of the dynamic conductivity whereas the conventional Darcy law velocity is a a linear function of spatial piezometric variation only with a constant hydraulic conductivity factor. Although, in the conventional calculations, it is possible to take into consideration the spatial hydraulic conductivity changes by finite zonations of conductivity, but still the main cause of groundwater velocity is due to the piezometric head changes. The new definition gives a convenient expression for the simultaneous changes of the hydraulic conductivity and piezometric level in groundwater flow velocity calculations. On the other hand, it is mathematically confirmed that initial groundwater movement takes place only after the exceedence of a certain piezometric gradient threshold value. This is tantamount to saying that even the hydraulic gradient is not equal to zero there may not be groundwater movement which is an absurd conclusion with the conventional definition of groundwater velocity by the Darcy law. The new definition takes into consideration various non-linear flow possibilities in the groundwater studies.