Comment by schoen

While Catalan speakers would be very unlikely to say "Catalan Spanish", there is a conception that there are many "lenguas españolas" (Spanish languages, as in languages that are part of the country of Spain). In this formulation even Basque is a "Spanish language" (as a language of Spain), even though it isn't linguistically related to Castilian Spanish.

Notably, the constitution of Spain uses this phrasing in its article 3:

1. El castellano es la lengua española oficial del Estado. Todos los españoles tienen el deber de conocerla y el derecho a usarla.

2. Las demás lenguas españolas serán también oficiales en las respectivas Comunidades Autónomas de acuerdo con sus Estatutos.

3. La riqueza de las distintas modalidades lingüísticas de España es un patrimonio cultural que será objeto de especial respeto y protección.

In English:

1. Castilian is the official Spanish language of the state. All Spaniards have the duty to know it and the right to use it.

2. The other Spanish languages are also official in their respective Autonomous Communities, in accordance with their Statutes.

3. The richness of the different linguistic modalities of Spain is a cultural heritage which shall be accorded particular respect and protection.

I've heard a minority of (seemingly highly educated) people prefer to say "Castellano" instead of "Español", maybe as a deliberate reference to this concept.