Net income is what is left after every cost: making the product, running the business, interest, taxes, and one-offs. It is the bottom line, the most quoted profit number, and the easiest to bend, in legal ways worth knowing.
One-off gains land here: sell a warehouse and the profit drops straight into net income, flattering a year the actual business did not earn. Depreciation choices work quietly: calling a machine's life fifteen years instead of ten shrinks the yearly expense and lifts profit. And timing games: choosing the convenient year to write down an asset, or releasing reserves set aside for expected losses back into profit (both are explained in their own glossary entries).
The defense is one habit: read net income next to operating cash flow, the cash that actually arrived. Cash consistently below reported profit means those earnings deserve suspicion.