What is "elementary charge"

n. (context physics English) The electric charge on a single proton

The elementary charge, usually denoted as or sometimes , is the electric charge carried by a single proton, or equivalently, the magnitude of the electric charge carried by a single electron, which has charge . This elementary charge is a fundamental physical constant. To avoid confusion over its sign, e is sometimes called the elementary positive charge. This charge has a measured value of approximately In the cgs system, e is .

The magnitude of the elementary charge was first measured in Robert A. Millikan's noted oil drop experiment in 1909.