Trapeze width refers to the actual catchzone. For example some yoyos might have a 45mm “width” but only a 43mm “trapeze width”
Gap width is the width of the gap between the two response pads.
Trapeze gap on the other hand is not a term, which was what jhb was referring to. Stating 4.7 though, it was obvious that notathrower was talking about gap width so it was pretty pointless to bring it up at all.