Its the height -- most standard house shoes dont have a lot of room between the sole and the ceiling of the shoe (Im not a show professional so Im sure theres a technical term for "ceiling of the shoe". the battery lasts long and the sound is great for gaming and listening to music. 5-2-2016, has been a few days of constant use. They?re well made in my opinion and I want these to be in stock forever ???? Anyone who likes rhythm games will like this, it is just as addictive as Beat Saber IMO. - Sound quality is very good (pretty balanced, bass not too boomy, good clarity). Delivered quicker than expected. My shoe size is size 7 and I ordered a large and fits well. Do not charge accessories. Dont blink, or youll miss which pod to tap!