This is the 2965th most frequent Russian word.
губ
"Губ" is not a standalone word in modern Russian; it is a root or part of words related to "губа" (lip).
In this sentence, 'губ' is used in its literal sense to refer to a part of the body, specifically the lips.
Она коснулась его губ.
She touched his lips.
In this context, 'губах' is used metaphorically as part of an expression meaning a smile appears on one's lips.
У девушки на губах играла улыбка.
The girl had a smile playing on her lips.
Here, 'губ' is part of a figurative phrase emphasizing direct communication.