[Alfonso]

According to DRAE, tilde is any mark you write over a letter to distinguish it from another letter, including the "ñ" mark and, especially, the marks you use for acentuación.
So tilde is both. But it's completely unnecessary to refer to the mark over the "ñ" as tilde. On the other hand, it's really common to call tilde to the acento ortográfico, as many people have been taught in Spain.
I know scholarship tradition varies from country to country but, according to what your friends say, how do they distinguish acento from tilde?: Todas las palabras tienen acento, pero sólo algunas llevan tilde.