A more thorough explanation:

An Employee's Withholding Allowance Certificate is a form that an employee fills out to let their employer know how much federal income tax to withhold from their paycheck. This form is also known as a W-4 form.

For example, if an employee is married and has two children, they may claim four allowances on their W-4 form. This means that their employer will withhold less money from their paycheck for federal income tax because they have more dependents.

Another example is if an employee starts a new job, they will need to fill out a new W-4 form for their new employer. This form will help their employer determine how much federal income tax to withhold from their paycheck.