He means barrel length.

I have been shooting a Benelli Super 90 with a 21 inch barrel since 1995 and have had no trouble killing anything that flies or deer and hogs with buckshot, but I like a short barrel. My Dad had a 28 inch barrel on his Benelli but liked my shorter barrel better, so I got him a 24 inch barrel which he likes alot better.

Generally, trap guns have longer barrels, but since you are going to use the gun for upland hunting too, I would recommend a 26 inch barrel. I will admit that the longer sight plane is helpful on trap and skeet.