As with all such words, usage varies. The most logical definition is: "someone who makes music as a habit". This includes composers, producers, amateurs, and of course "horrible musicians". To be called a musician is not a particular honour, and to call oneself thus is not a boast.

On the other hand, someone who is merely "musically talented" but never makes or made music will scarcely qualify – the Oxford Dictionary is wrong.

Neither will someone who sings in the bathroom without expecting anyone to hear it. And of course, there are fringes in the definition of "music".

Colloquially, the term is sometimes confused with "instrumentalists", not necessarily because vocal music is considered inferior. For example, sloppy journalists may write about "singers and musicians" at an opera house, presumably believing that the singers are more important than the instrumentalists.

Those who worry too much about words are often struck with an inferiority complex or other problems they do not dare to address properly.