Names given to the Spanish language
Formally speaking, the national language of Spain, the official Spanish language, is the Castilian language (as opposed to regional Spanish languages like Galician, Catalan, Asturleonese and Basque). As such both names, "español" and "castellano", have distinct and independent meanings that may be required for clarity in some specific contexts.
Generally speaking, though, both terms can be used to refer to the (national) Spanish language as a whole, with a preference for one over the other that depends on the context or the speaker's origin. "Castellano" (as well as "Castilian" in English) has another, more restricted, meaning, relating either to the old Romance language spoken in the Kingdom of Castile in the Middle Ages, predecessor of the modern Spanish language, or to the variety of Spanish nowadays spoken in the historical region of Castile, in central Spain.
Equatoguinean Spanish
Equatoguinean Spanish () is the variety of Spanish spoken in Equatorial Guinea. This is the only Spanish variety that holds national official status in Sub-Saharan Africa. It is regulated by the Equatoguinean Academy of the Spanish Language and is spoken by about 90% of the population, estimated at 1,170,308 for the year 2010 (though population figures for this country are highly dubious), all of them second-language speakers.