What it measures
Return on Equity is net income divided by shareholders' equity, expressed as a percentage. It answers a different question than net profit margin does: not "how much of revenue becomes profit," but "how hard is shareholders' own money working."
Two companies can have identical profit margins and very different ROE if one uses debt to amplify its equity returns and the other doesn't, worth reading alongside the balance sheet picture, not in isolation.
A worked example
A company with 800,000,000 in shareholders' equity reports net income of 196,800,000 for the year. ROE: 196,800,000 / 800,000,000 = 24.6%.
How Kobo & Cents uses it
ROE is one of the three profitability metrics, and it's the single most commonly cited driver in the explainability panel's reasoning, "ROE is strong and trending up" is a real, frequent sentence there, because it's often the clearest single signal of whether a company is actually compounding value for the people who own it.