Luso- is a Late Latin prefix used to denote Portugal/Portuguese, in conjunction with another toponym or demonym.

A Lusophone is someone who speaks the Portuguese language, either natively or as an additional language. As an adjective it means 'Portuguese-speaking'. The Lusosphere or Lusophony, is the totality of Portuguese speakers around the world, and the influence of the language and culture.

The term is derived from Lusitania, the name of a Roman province in the Iberian Peninsula, which encompassed most of modern Portugal.

More Info: en.wikipedia.org