A 401(k) is a retirement savings plan that is sponsored by an employer. It lets workers save and invest a piece of their paycheck before taxes are taken out. Taxes aren't paid until the money is withdrawn from the account.
In other words, employers can set up a savings plan for their employees, which allow for pre-tax contributions.
It is important to note that your employer is the party who establishes the plan, but you can affect who contributes
IRAs, unlike the popular 401K or the lesser known 403B are individual accounts, not set up by employers. In fact, IRAs are often used by self-employed individuals. That being said, there are several types of IRA accounts, each with eligibility restrictions based on your income or employment status.
it can be used to complement a 401k or 403b plan if you have that option at work, or as a stand-alone method of savings for retirement.