Define pants role and list an example from a famous opera of the Classical era?

It seems like you might be asking about the "pants role" in opera, rather than "pants role".

A pants role is a role in opera written for a female singer but performed by a woman dressed as a man. This was common practice in the 17th and 18th centuries, as women were not allowed to perform on stage in many countries.

A famous example from the Classical era is Cherubino in Mozart's *The Marriage of Figaro*. Cherubino is a young, lovestruck page who is constantly getting into trouble for his flirtatious nature.

Here are some other examples of famous pants roles from the Classical era:

* Rosina in Rossini's *The Barber of Seville*

* Zerlina in Mozart's *Don Giovanni*

* Despina in Mozart's *Così fan tutte*

These roles are often written to be youthful and energetic, with a touch of mischief. They provided a great opportunity for female singers to showcase their talent and artistry, even if they had to disguise themselves as men to do so.