How is a devidend named, that under a line?

In a fraction under a line a divizor is written. He is named denominator. If you must find the denominator of fraction, it is needed to search him under a fractional line. Type, how under a bed to glance. All denominators are always hidden under a fractional line, as under a bed. As a denominator there can be both numbers and whole mathematical expressions, sometimes very large.