What do a direct electrical current is different from an alternating current because only the direct electrical current means?

In Direct Current, electrons flow from the negative pole of the electrical source, through the load, to the positive pole of the electrical source. Current is constant as there are no variations in voltage over time in the circuit. Voltage and current are measured by directly measuring the voltage and current in the circuit.

In Alternating Current, electrons also flow from the negative pole of the electrical source, through the load, to the positive pole of the electrical source. However, the polarity of the poles changes +/- to -/+ to +/- , alternating polarity over and over again. This causes the direction of the electrons in the circuit to change each time the source poles change polarity. Current and voltage are not constant in an AC circuit as they vary with the waveform generated by the electrical source. In many, but not all cases, voltage and current are measured by the RMS (root-mean-square) method as directly reading the peaks of the AC waveform will not indicate the correct amount of energy in the circuit.