It is a Serbian word, for the living offspring of a vampir and a mortal. The belief goes that the gypsy "mulo" was said to be a spirit of the dead person. It was also believed that the male mulo was capable of impregnating living women, most often their grieving widows. The resulting child was variously called a "vampijorivic", a "vampiric", or a "lampijerovic", all of which mean "little vampire" ... another name for such an offspring is "dhampir".
There are various variations of this, but the most common is that the impregnated female does not come to full term and the baby is lost. In other instances, the mother comes to term and gives birth to a stillborn. In extremely rare cases will a dhampir be born and grow to adulthood.
Dracula used the term to refer to someone who cannot be turned into a vampire.
(And to answer what may be another question, the words "vampeal" and "dunpeal" are mistranslated Japanese "danpiru" from Vampire Hunter D, who is a Dhampir.)