An estimate is an approximation used to price an insurance contract. Some coverages use proxies like expected revenue in the upcoming year as a way of determing the amount of risk an insurer may take on. It is understood that these are just guesses, and at the end of the year, the insurer may ask for actual numbers and invoice/refund the premium difference due to the discrepancy between the estimate and the actual numbers. This is very common in commercial general liability policies, or commercial automobile fleet policies.