The current that goes in a terminal is equal with the one that flows out from the other terminal.
Figure 3: The current through a dipole
It corresponds to the quantity of electric charge 
that traverses the dipole, during the unit of time:
A current of one ampere (1 A) corresponds to the passing of an electric charge of one coulomb (1 Cb) during one second. The reference sign for the flow of the current can be chosen arbitrarily: if the current passes in the chosen sense, it's value (intensity) is positive; if it passes contrarily as the chosen sense, it is negative.
Note: Taking into account that in the usual metallic conductors, the charge carriers are the electrons, that have negative charge, the flow from A to B of a positive current of 1 A, corresponds physically, to the flowing from B to A of the number of electrons whose added charge is -1 Cb, during one second.
