I have seen this word being used many times, following it usually, but not always terrible English. Is it a proper use?
One example: http://libopencm3.org/docs/latest/stm32l1/html/group__i2c__defines.html Here the documentation points a file (and many other on the left) which include various definitions, and files are called '... defines'
You will see this kind of thing in some software areas: inserts, deletes, etc.
In "ordinary" English these are not traditionally considered words. But in the realm of software, at least, such words are common, including in technical documentation. And language evolves...
No doubt the same is true for defines. Typically such a use comes from the existence of a programming keyword (in this case, "define" or "DEFINE"). It is natural to talk about code that uses it as a define etc.
As for whether using such a term is "proper": that's primarily opinion-based. Proper to whom, in what context, etc.
