Vector_type?

I have met the following code:

#ifndef vec_t
typedef VECTOR_TYPE vec_t;
#endif

Is VECTOR_TYPE a program default word or uer defined word?

I searched MSDN and found nothing for VECTOR_TYPE. Searching with google, I found this:

System constants

The following constants are used by the various functions of the system to signal certain conditions. Internally, they are represented numerically, although, in general, their exact value is unimportant and may be changed in future versions. In the rare circumstance that you need to know their values, simply type the constant as an expression.

VECTOR_TYPE

A constant defining an object of type vector.

Thank you for your reply