A step-through frame removes the top tube, so you walk into the bike rather than swinging a leg over the back of it. It sounds like a small thing. It is not — it is often the difference between a bike that gets used every day and one that stays in the shed.
It matters most if you have limited hip mobility, if you are shorter than the frame really wants, if you stop and start constantly in traffic, or if the bike is usually loaded with a rack, a basket or a child seat.
