Amateur Radio Manual/What is Current
To make electrons flow in a conductor, we first must supply some form of electromotive force (potential difference). This can be achieved attaching the conductor to some source (generator), like a battery or a power supply.
Current, then, is the rate of flow of electrons through the conductor (with unitary diameter), measured in amperes (A) after the French scientist André-Marie Ampère. In formulae, current is represented by the letter I. That's a capital eye.
The ampere is a large measurement so we usually refer to milliampere (mA), being 1/1000 of an ampere, in small measurements.
One ampere is equivalent to
charged particles (or 1 coulomb) moving through a unitary section conductor in one second.
Current is measured with an ammeter.