In biology, depolarization is a decrease in the absolute value of a cell's membrane potential. Thus, changes in membrane voltage in which the membrane potential becomes less positive or less negative are both depolarizations. In neurons and some other cells, a depolarization large enough may result in an action potential. Hyperpolarization is the opposite of depolarization, and inhibits the rise of an action potential. The rising and falling phases of such an action potential are often imprecisely also called depolarization and hyperpolarization, respectively.
If a cell has a resting potential of -70mV and the membrane potential changes to -50mV, then the cell has been depolarized.