Allusion:
an expression designed to call something to mind without mentioning it explicitly; an indirect or passing reference.
Which is what this line is. It's a beautiful reference and I never actually read this work fully, but I am assuming that this is Romeo calling out to Juliet, saying that she is the same pleasant sensation that he gets from the smell of a rose, lifting him to a level of happiness and euphoria that is easy for Juliet to understand instantly.
