You can of course define "perfection"--consult a dictionary for an example.
And it is easy enough to come up with an example of perfection: a "perfect square" has four sides of exactly equal length with all interior angles at exactly 90 degrees. Everything else is less perfect of a square (and the above is the mathematical definition of a perfect square, so there's really no relativity about it).
Questions about what is perfectly good, however, run into all the problems that are encountered when asking about anything to do with "good", which is that people don't agree on what good is and generally do not manage to come into agreement via discussion.
However, if you postulate a function that can evaluate how good something is,
G(.), you can use it to come up with a pretty natural version of what "perfection" means in that context, i.e.
x is perfect if there is no conceivable
y of the same kind of thing as
x (let's assume we know how to determine this) such that
G(y) > G(x). This is essentially the notion of perfection used in Anselm's ontological argument for God.
(Whether such a function is possible is another question. You probably would end up with a family of such functions, and then you would start talking about perfect-according-to Gk for a particular