best i can say about it is this:
the word means Union
the act of Yoga is a meditation and prayer
very often the way it is taught
is as a stretching excersize to keep fit
which by far misses the meaning
in any pose that you do
try doing the most simple one you remember:
mountain pose; corpse pose
your intention should be to be present with every aspect of yourself
every muscle
each sinew
everything feeling and thought
and then further
to be present with every aspect of everything
thus, God
-- traditional yoga is from a hindu perspective
which gives the divine many different points of reference (they being polytheistic)
but the eventual goal, even then, is to become fully present with all existance
that is what yoga is about
and it makes those very difficult and strange positions much more interesting:
understanding your place in eternity
and what to do there...