A transformer will have several ratings - voltage, current, environmental conditions like temperature, etc. They are usually presented as either single figures or a range of figures over which normal operation can occur.
Sound like you are talking about power transformers used in electricity distribution so this question should be in Power Design category.A figure like "rated current" would mean that the transformer could supply that current 24/7 without getting too hot or otherwise rising damage.Maximum ratings are the figures that should not be exceeded, and should not be approached for anything other than a short time.Absolute maximum ratings are sometimes used in place of Maximum ratings , and if exceeded should result in an inspection if no obvious damage is evident.