Mojo

A mojo was among the things that Clara Oswald lost as a child. She eventually got it back. Exactly what a mojo was was not specified. (WC: The Bells of Saint John: A Prequel)

Behind the scenes
This could refer to "the Mojo magazine", a music magazine that has been published in the UK since 1993.

This could also refer to an Austin Powers reference. In , his mojo is the source of his sex drive. It's possible that this is what the Doctor thought she meant, which would explain his response.