Even if you're not an employee, there are many different ways to earn money: driving people around, blogging, being an independent distributor/consultant or business owner, and more. The IRS generally considers those types of income to be self-employment income.
Sometimes when you're self-employed (whether as your main source of income or on the side), you may receive 1099-K, 1099-NEC, or 1099-MISC. If you don't, you're still responsible for recording your income/expenses for tax purposes. All of this income, whether it's on a 1099-K, 1099-NEC, or 1099-MISC or not, needs to be reported on your tax return.