What is "application-defined clip distance"?

I ran accross this symbolic constant in the glGet() spec:
params returns one value, the maximum number of application-defined clipping distances. The value must be at least 8. symbolic constant that "

“GL_MAX_CLIP_DISTANCES” I cannot find explained in any documentation online.

Does anyone know what it is or what a clip distance is exactly?

It means that you can define at max 8 clipping planes in your applications.

How comes that you haven’t found explanation for the GL_MAX_CLIP_DISTANCES?

The user clipping is an extremely useful feature. gl_ClipDistance[i] - are values written by vertex shader in order to determine the distance from the clipping plane. The value itself is not important but the sign of that value.

Thank you Aleksander I did not know about the gl_ClipDistance[] built-in variable.
All I knew was that the near & far clip planes were a result of setting up a projection matrix.