The tilde is a common diacritical mark. I wrote to Luis Verano, of the University of Oregon, about it recently, and here is what he said.
One of the diacritical marks in Spanish is the tilde. When placed over the letter n (ene), the tilde creates a new letter—the ñ (eñe)—which produces the palatal nasal sound ny, as in the word señora or señor. Ramón Gómez de la Serna (1888–1963), a writer from Spain, referred to the ñ jokingly as “una n con bigote” (an n with a mustache). The ñ is an entirely different letter, however, and words that begin with ñ appear in a separate section in dictionaries.