The Hodgkin-Huxley model is a mathematical model that describes the generation and propagation of electrical signals in neurons. It consists of nonlinear differential equations that describe the voltage-dependent ionic currents that flow across the neuronal membrane. The model includes separate voltage-gated ion channels for sodium and potassium ions that allow the currents to change over time based on the membrane potential. The model can be used to simulate the membrane potential over time in response to an applied electric current stimulus.