What defines one ampere of electric current?

One ampere is defined as the flow of one coulomb of electric charge per second through a conductor.

Mathematically:
I = Q / t

where:
I = current (amperes)
Q = charge (coulombs)
t = time (seconds)

So,
1 ampere = 1 coulomb / second

This means that if 1 coulomb of charge passes through a cross-section of a conductor in 1 second, the current is said to be 1 ampere.

The ampere (A) is the SI unit of electric current and is a fundamental unit in electrical measurements.