Noun
step-through (plural step-throughs)
(chiefly attributive) An open space in an otherwise solid object through which a person can step or walk.
A motor-scooter has a step-through frame, also known as an "open frame".
Besides the traditional diamond frame men's bicycle, models included a step-through frame 3-18 "Ladies Standard" and a 5-17 "Boy Scout" for youth. Source: Internet
Because of its persistent image as a "women's" bicycle, step-through frames are not common for larger frames. Source: Internet
The M-65S was a M-65 with a larger tank that eliminated the step-through feature. Source: Internet
This design, referred to as a step-through frame or as an open frame, allows the rider to mount and dismount in a dignified way while wearing a skirt or dress. Source: Internet