side-top
Having sex while the woman lays on her back and the man screws her while on his side and part way on top, the woman's leg is usually pulled up so her knee is near her chest.
"I like to have sex side-top with my wife."
Top Side
The side on top of you. Yes that is a side also. Just like left side and right side.
"...and i'm telling you, there is a freaking top side. You got it? Like, what is the top of a box called? The top side!"