What it is
Net income is the final number on the income statement — what's left after everything has been paid: COGS, operating expenses, interest on debt, and taxes.
It sits on the last row of the statement, which is where the nickname bottom line comes from.
Why people watch it
Net income is the number that flows through to shareholders. It's used to compute EPS (Earnings per Share), funds dividends, and pays down debt or fuels new investment.
A loss (negative net income) means the company spent more than it took in this period. Some early-stage companies run losses for years on purpose; others have a one-off bad quarter.