What is the name of the type of bicycle frame with a low top tube, often called a 'step-through'?

The type of bicycle frame with a low top tube, often called a “step-through,” is a step-through frame.

Its defining feature is a low or absent top tube, which reduces standover height. A rider can mount and dismount by stepping through the frame rather than swinging a leg over a high crossbar. That makes the design practical for utility bikes, city bicycles, delivery bikes, folding bikes, and riders with limited agility.

Historically, these frames were often marketed as “ladies’,” “women’s,” or “girls’” bicycles because they accommodated skirts and dresses. Those labels have become less common because the frame style is suitable for riders of any gender. A step-through is not the same as a recumbent, which places the rider in a laid-back seating position, or a cargo bike, which is designed to carry loads.

A mixte frame is a related variation: it uses twin tubes running toward the rear axle while retaining the easy step-through geometry. Compared with a traditional diamond frame, a step-through may need thicker tubing or extra bracing to achieve similar stiffness.