Anyone can use any grammatical terms to refer to grammatical phenomena. Some terms are almost universally accepted, some are used by a handful of people only. Actually, discrepancies are not at all uncommon. For instance,
he is usually called the subject in the following sentence.
He was seen at the station.Yet in actual fact
he is the
object of seeing.
He did not perform the seeing at all.
He is simply called the subject because in an affirmative clause the subject normally precedes the main verb and in addition to that,
was is the correct conjugated form of
to be after
he. In many other languages, Finnish for example, the
object form of
he (in English:
him) is required in a sentence like the one above.
In other words, terminology and actual usage don't always go hand in hand.
By the way,
Central Park is the subject of the main clause only (
Central Park is beautiful and green.) The subordinate relative clause has a subject of its own:
which (or:
you).
Cheers
CB