Estimated Tax

What Does Estimated Tax Mean?
Periodic advance payment of taxes which are based upon the amount of income that is earned and the amount of estimated tax liability that will be incurred as a result. Estimated taxes are assessed on income that is not subject to any type of withholding, which includes self-employment income, dividend income, rental income, interest income and capital gains.

Investopedia explains Estimated Tax
Estimated taxes are usually paid on a quarterly basis. If the estimated taxes that are paid do not equal at least 90% of the taxpayer's actual tax liability (or 100% or 110% of the taxpayer's prior-year liability, depending on the level of adjusted gross income), then interest and penalties are assessed against the delinquent amount.