What are you talking about, Leigh?
When a dancer pulls the foot of her gesture leg up to the knee of her support leg, this can alternately be called retire or passe. The two look exactly the same but are, in fact, quite different.
Huh? What's the difference?
Think of retire as a position while passe is an action. Retire means to withdraw or "draw up." Passe means passing, as if you are passing through something.
Still doesn't mean anything to me. Why do I need to know this?
It's important to understand the difference so you know when to apply each to what you're doing. For instance, in an adagio, you might think of the gesture leg moving through passe as you develop it en avant. In this case, it is an active part of the movement, rather than a static pose. However, if you were performing a pique turn, you would bring the leg up to the position of retire and think of holding it in that position as you pirouette.
Speaking of pirouette...which am I using?
Both. Kind of. Simultaneously. First, regardless of your preparation for your pirouette en dehors, you take a demi-plie and spring up to your releve on the support leg. The gesture leg draws up to retire and you think of this as the shape in which you will be rotating. BUT! During the turn, you need to keep that gesture leg active so while it is in the retire position, it is actually passe in that the knee is continuing to press back (as you "open the door") and maintaining turnout at the top of the thigh. It does indeed "pass through" just before you finish the turn and roll down to your final pose.
Anything else you want to say on this topic?
Yes! No matter which you word you use, be sure to keep the hip down, avoid sickling the foot of the gesture leg, and pull up the quads/kneecaps/hamstrings of the support leg. And one more thing...