“Belly” and “roll” are terms used to describe the lapels on a jacket and there seems to be some confusion about what they mean.
When we say a lapel has a belly to it, we mean there is a curve in the edge of the lapel as it approaches the button. The opposite would be a straight edge. There is a notion that some lapels are given a concave edge but this is just an optical illusion or perhaps poor workmanship; the run of the grain, or a stripe, would look ridiculous if the edge were actually cut in a concave shape, but the lack of any belly could make the edge look concave. English tailors often produce garments with a pronounced belly, others, such as Ralph Lauren, prefer a very straight line. I, personally, prefer to cut the edge with a slight belly but then work up the edge of the facing so that any stripe follows the edge and does not run off. The effect is especially pronounced on wider lapels, especially peaks.
This is a lovely garment by Tom Ford but notice how the plaid runs off the edge about halfway down the lapel. I find this visually distracting.
My preference is to work up the facing with the iron so that it looks straight, but actually has a belly to it, like on this double-breasted coat I made many years ago.
Now on to “roll”. We use a technique called “pad stitching” to build in a permanent shape to the lapel, by rolling the layers as we stitch invisibly through. More on this in a later post. A coat front which I padded by hand can be seen here.
The result of a well-padded lapel using a good quality canvas can be seen in this lovely garment by @silviovista_official