The two-step is a step found in various dances, including many folk dances. It seems to take its name from the 19th century dance related to the Polka.
A two-step consists of two steps in approximately the same direction onto the same foot, separated by a closing step with the other foot. For example, a right two-step forward is a forward step onto the right foot, a closing step with the left foot, and a forward step onto the right foot. The closing step may be done directly beside the other foot, or obliquely beside, or even crossed, as long as the closing foot does not go past the other foot.
Some types of two-step, or related steps, are named "lock step".