In our experience, "one size fits most" generally means the item has a lot of stretchy material that will allow for a broad number of sizes to fit in it. We've sometimes found this also means the items are made cheaper, and don't always have the same stitching/build quality as items that come in more specific sizes. Obviously, the price of the item plays into this as well. However, if you're thinking of dropping a lot of money on a nice piece that "fits most", you may want to talk to someone who owns it, or look for better-built products.