Nadie vs. ninguno
While both nadie and ninguno can be translated as no one or nobody in Spanish, they are not interchangeable. The main difference lies in what they refer to and how they are used grammatically. Nadie refers exclusively to people in a general sense, while ninguno means not one and can refer to either people or things, often from a specific group.
Nadie
A1Nadie is a pronoun that means no one or nobody. It refers exclusively to people and is invariable, meaning it does not change for gender or number. It is the most direct and common way to say nobody.
Nadie vino a la fiesta anoche.
(Nobody came to the party last night.)
No vi a nadie en la oficina.
(I didn't see anyone in the office.)
No le cuentes este secreto a nadie.
(Don't tell this secret to anyone.)
Ella no quiere hablar con nadie ahora mismo.
(She doesn't want to talk to anybody right now.)
¿Quién llamó? Nadie.
(Who called? Nobody.)
Ninguno
A2Ninguno acts as an adjective or a pronoun meaning not one, none, or any. It can refer to people or things and must agree in gender with the noun it modifies or replaces (ninguno for masculine, ninguna for feminine). Before a masculine singular noun, it shortens to ningún. When it refers to people, it specifically means not one person from a particular, known group.
Ningún estudiante entendió la lección.
(No student understood the lesson.)
No tengo ninguna camisa limpia.
(I don't have any clean shirts.)
De todos mis amigos, ninguno vive cerca.
(Of all my friends, none of them live nearby.)
¿Cuál de estos pasteles quieres? No quiero ninguno.
(Which of these cakes do you want? I don't want any of them.)
Le pregunté a los dos testigos, pero ninguno vio nada.
(I asked the two witnesses, but neither of them saw anything.)
No tengo ningunas ganas de ir al cine.
(I have no desire whatsoever to go to the movies.)
Summary
In short, use nadie as the general term for nobody or no one. It only refers to people and never changes its form. Use ninguno (or ninguna/ningún) when you mean not a single one from a specific group of people or things. Ninguno must always agree in gender with what it refers to.