What it measures
Shareholders' equity is total assets minus total liabilities, the company's net worth on its own books. It's the accounting-defined version of "what's actually left over" once every obligation is subtracted from everything the company holds.
It grows when a company earns and retains profit, and shrinks when it takes losses or pays out more than it earns. A steadily growing shareholders' equity over several years is a reasonable sign a company is actually building value, not just generating revenue.
A worked example
A company holds 2 billion in total assets and owes 1.2 billion across every liability, loans, payables, everything. Shareholders' equity: 2,000,000,000 − 1,200,000,000 = 800,000,000.
How Kobo & Cents uses it
Shareholders' equity sits in the equity category alongside book value, and it's also the denominator behind Return on Equity in the profitability category, worth reading together with that metric, not only on its own.