What is the meaning of Step-up?

That increases in stages. (Can we add an example for this sense?)

That increases a voltage.

A workout movement wherein one leg stands on an elevated surface and lifts in the concentric part the rest of the body up onto it to target – depending on angle and starting distance of the other leg and weights applied by the arms – the femoral and gluteal muscles variously.

An increase.

Source: wiktionary.org