In BJT as the B-C reverse bias voltage increases, the B-C space region width increases which $x_B$ (i.e neutral base width) > A change in neutral base width will change the collector current. A reduction in base width will causes the gradient in minority carrier concentration to increase, which in turn causes an increased in the diffusion current. This effect is known as base modulation as early effect.
In JFET the gate to source voltage that must be applied to achieve pinch off voltage is described as pinch off voltage and is also called as turn voltage or threshold voltage.
In LASER population inversion occurs on the condition when concentration of electrons in one energy state is greater than that in lower energy state, i.e a non equilibrium condition.
In MOS capacitor, flat band voltage is the gate voltage that must be applied to create flat ban condition in which there is no space region in semiconductor under oxide.
Therefore BJT : Early effect
MOS capacitor : Flat - band voltage
LASER diode : Population inversion
JFET : Pinch-off voltage