Generalised h-parameter model of an NPN BJT. The term "x" in the model represents a different BJT lead depending on the topology used. For common-emitter mode the various symbols take on the specific values as:

x = 'e' because it is a common-emitter topology
Terminal 1 = Base
Terminal 2 = Collector
Terminal 3 = Emitter
iin = Base current (ib)
io = Collector current (ic)
Vin = Base-to-emitter voltage (VBE)
Vo = Collector-to-emitter voltage (VCE)and the h-parameters are given by –

hix = hie – The input impedance of the transistor (corresponding to the emitter resistance re).
hrx = hre – Represents the dependence of the transistor's IB–VBE curve on the value of VCE. It is usually very small and is often neglected (assumed to be zero).
hfx = hfe – The current-gain of the transistor. This parameter is often specified as hFE or the DC current-gain (βDC) in datasheets.
hox = hoe – The output impedance of transistor. This term is usually specified as an admittance and has to be inverted to convert it to an impedance.
H-parameters.gif
H-parameters.gif: The original uploader was Rohitbd at English Wikipedia.
derivative work: Inductiveload (talk)