What is the meaning of Step-up?

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.

A phenomenon whereby the growth in market value of an asset or investment is not taxed under certain circumstances, generally involving buying and holding until the buyer's death, followed by inheritance.

Source: wiktionary.org