"Identical triplets" refers to a situation where there are three siblings who look exactly the same because they were formed from a single fertilized egg that split into three parts. Full definition
Three strangers are reunited by astonishing coincidence after being born identical triplets, separated at birth, and adopted by three different families. (metacritic.com)
[2] Nevertheless, only 4 sets of identical triplets were reported in the U.S. during 2015, about one in a million. (en.wikipedia.org)
Identical triplets come from a monozygotic pregnancy, three fetuses from one egg. (en.wikipedia.org)