Awning

This type has a hinge at the top and is usually rectangular and short. In Bangladesh, you'll find awnings in most bathrooms because a window near the top of the wall is great to let out hot air. Keep in mind this means only partial ventilation. But above doors or showers or other window frames, the awning is great for letting in sunlight and air.

Bay/Bow

Delicate and ultra-chic, bay windows can cover an entire wall, right to left, top to bottom. These windows open outwards, giving your more space inside the house. While perhaps not a window-style by itself, bay windows are a combination of stationary windows in the middle and double-hung or casement windows on either side. Given their size, these could be difficult to maintain, which would completely defeat the purpose of having such elegant windows in the first place.

Casement

A casement window either has a hinge on its right or left side. It usually has a crank handle that opens it outwards.

The casement gets A+ for ventilation as well as low air leakage because the window can open all the way out or seal all the way around when shut. It also gets bonus points for excellent noise cancelling. 

On the downside, the crank tends to get annoying with time—too much effort to open. Casements are also suited for mainly outer walls.

Fixed/Picture

Fixed windows have no moveable parts, but they commonly come in various shapes and sizes. A large picture window can let in maximum sunlight and views of the outside and a small one can brighten up a staircase. If you badly don't want a draft in your room, this is your guy. Since it can't be opened, you won't get any ventilation and it'll need to be cleaned from the exterior. 

Single- or double-hung

The double-hung consists of two moveable panels that both slide up and down, while the single-hung consists of a moveable bottom panel and a stationary upper one. 

Cool fact about the double-hung: opening both panels at the same time creates a natural convection—hot air escapes out the top and cool air enters through the bottom. Unlike casements, these windows don't open outwards or inwards, but some might find the horizontal rail right in the middle quite ugly (think: train windows). 

Slider

This window does exactly what it says. Sliders have one or two horizontally moveable panels. They're more common in modern-day houses and work great for verandas and patios. 

Whatever you pick, remember that windows can always be decorated and customised to match the colour scheme of your room or the style of your décor. So spend an afternoon window shopping and hand in those cob-webbed British-era grills for something shiny and fabulous.