Multiple birth.

A multiple birth occurs when more than one fetus is carried to term in a single pregnancy. The preceding pregnancy is called a multiple pregnancy. Different names for multiple births are used, depending on the number of offspring. Common multiples are two and three, known as twins and triplets, respectively. These and other multiple births occur to varying degrees in most animal species, although the term is most applicable to placental species. 

Terminilogy:
Two offspring – twins
Three offspring – triplets
Four offspring – quadruplets
Five offspring – quintuplets
Six offspring – sextuplets
Seven offspring – septuplets
Eight offspring – octuplets
Nine offspring – nonuplets
Ten offspring – decaplets
Eleven offspring – undecaplets
Twelve offspring – duodecaplets

  

 By: Natalia Marquina Rubio.