A moat is a durable competitive advantage — something that stops rivals from bidding away a company's profits. Brands, switching costs, network effects, scale, patents. The trouble is you can't put a moat on a balance sheet, so investors look for its footprint instead.
The clearest footprint is return on capital. Return on equity is net income divided by the equity owners have in the business; return on invested capital is after-tax operating profit divided by the debt and equity funding it. Either way the question is the same: for every dollar tied up in this company, how many cents a year does it earn? A business earning 30–40% on capital year after year is doing something competitors can't copy — otherwise competition would have dragged those returns down toward the 8–10% it costs to fund the business. Sustained high returns on capital are the number's way of saying *moat*.
The key word is sustained. One good year is luck or a cycle; a decade of high returns is structure. This site shows the multi-year trend, not a single figure, and sets it against the company's own cost of capital — because 20% returns mean nothing if capital costs 25%, and 12% is excellent if capital costs 8%.
A moat also shows up in margins that don't erode: pricing power lets a company hold prices while costs rise. High returns on capital and stable margins usually travel together. Neither is proof — moats crumble — and this site will never tell you a moat is 'wide.' It shows you the evidence and teaches you to weigh it.