Large-signal modeling is a common analysis method used in electronic engineering to describe nonlinear devices in terms of the underlying nonlinear equations. In circuits containing nonlinear elements such as transistors, diodes, and vacuum tubes, under "large signal conditions", AC signals have high enough magnitude that nonlinear effects must be considered.[1]
"Large signal" is the opposite of "small signal", which means that the circuit can be reduced to a linearized equivalent circuit around its operating point with sufficient accuracy.