To estimate is to form an opinion or judgement concerning a degree of measurement or quality about an object or person; such as worth, value, size, weight, volume, etc.. By nature an estimate is subjective and its value depends on the expertise of the estimator. Although commonly used as a synonym for guess an estimate is expected to be close to the real quantifiable value.
Tradesmen, auctioneers or realtors may provide an estimate of the proposed cost of something, as a guideline for the ultimate price which is to be paid.
In statistics an estimate can be used to approximate the true values of something being analyzed, even when a full set of quantifiable data is not readily available. Such an estimate can be based on a variety of factors and relies on the expertise of the person computing the estimate.