This is a traditional wooden casement window with side openers.
The corner joints the window frame use draw-bored tenons (secured with tapered pins) inside slot mortises.
In the side opener frames, the corners use a sloped haunched tenon to increase the gluing area and the mechanical resistance to racking and twisting. The transom (median rail) uses a draw-bored tenon in a mortise, also secured with a pin. The frames of side openers are also rabbeted on the inside to receive the glass pane, and on the outside to rest on the complementary rabbet in the window frame.
