Triplets

My beginning poetry class is unsure
about tercets and triplets. They're both 
stanzas with three lines. The difference 

is that all three lines of a triplet rhyme. 
I ask, Who has triplets in their family? 
The girl who always sits front, center, 

raises her hand; she's one of a set 
of triplets. She looks slightly confused 
when I ask, Which one of you is here?