"Tomorrow is not Thursday."
Translation:Mañana no es jueves.
When you use a singular definite article, it always means "the". However, when you use a plural definite article, it can mean either the specific nouns or that noun in general. Here are some examples: Mañana no es el jueves = Tomorrow is not the Thursday. (using a specific Thursday) Yo corro los jueves = I run on Thursdays. (using Thursdays in general)