Line of Sight 0

In another thread the term “line-of sight” was used to illustrate the ability to see objects
Line of sight

1. the straight line along which an observer looks or a beam of radiation travels
I understand the principle involved, but what then is a "mirage"? Clearly, mirages are of objects not within the line of sight, yet we see the object as if it were straight ahead of us, but when we get there, the object is not there! How does this jive with the notion of "line of sight"?