What spell did Dumbledore use to protect Harry as an infant?

Dumbledore used a powerful charm to protect Harry Potter as an infant, rather than a specific spell. This charm, known as the Fidelius Charm, hid Harry from Voldemort's influence and attacks for the first eleven years of his life.

Here's how it worked:

* Secret-Keeper: Dumbledore designated himself as the Secret-Keeper for Harry's location. This means he was the only person who knew where Harry was living.

* Hidden Location: Harry was placed under the Fidelius Charm in the home of his aunt, uncle, and cousin, the Dursleys.

* Protection: The charm made Harry invisible to anyone who didn't know the secret of his location. Voldemort, as the one who was actively seeking Harry, was unable to find him.

The Fidelius Charm is a very powerful and complex spell. It required Dumbledore's extensive magical knowledge and skill to cast it effectively.