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Window Terminology 101


As with most construction-related projects, there is very specific terminology related to said project, and windows are no exception.

Being informed on all the different parts of a window will help you make important renovation or installation decisions while making it much easier to understand exactly what options you have when it comes to window design. Each part of the window plays its own role in ensuring proper use, insulation, and overall aesthetics.

Windows are a big part of the home and typically play a big role in the overall mood of a room. Not only do windows let sunlight into the living space, but they also allow for an instant sneak-peek into the natural beauty the outside world has to offer.

Windows come in all sizes, shapes, and styles, but the terminology remains the same. To further help our readers and customers comprehend all aspects of a home’s windows, we decided to create this easy-to-read terminology guide!

Window Terminology Explained

Common Parts Of A Window

  • Frame
  • Head
  • Sill
  • Jambs
  • Casing
  • Apron
  • Sash
  • Sash Lock
  • Grilles
  • Rail
  • Lift


The window frame may just be the simplest of terms on this list! The frame is the area encasing the glass window panes that connects to the wall. Window frames are typically crafted from wood or vinyl, depending on style preferences.

Parts of the frame include the jambs, head, and sill.


The head of a window frame is the top horizontal section running the full width of the frame and is the maximum height of the window.


Windows have both vertical and horizontal sash sections. These sections move with the window and are installed around all four sides of each moveable pane.

Sash Lock

This keeps your sash securely in place to prevent drafts or unwanted specimens from entering the home.


The place where the top sash and the bottom sash meet in the middle of a Double Hung window (or right and left sash in a sliding window) is called the rail or meeting rail.


The window sill is the lowest horizontal section of the frame and provides a firm surface for the sash to rest against when the window is closed.


The vertical sections along the side of the frame are called the jambs.


Decorative trim running below the window sill is called the apron and is for aesthetic purposes only. This section typically matches the window casing.

Jamb Extension & Casing

The window jamb extension and casing is the eye-catching decorative perimeter of the window that completes the space between the wall and window frame or jamb. Many people refer to the casing as the ‘trim’ and are typically used interchangeably.


Grilles are the grid-like pattern of wood, vinyl, or aluminum most commonly used on windows today. While grilles may seem to divide the windowpane into a grid-like pattern structurally, they are actually situated either on the outside of the glass or in between the panes and are purely decorative.


Need a little extra help opening a window? A lift, or small handle affixed to the bottom sash, is a quick and easy solution while adding a bit of character to the window itself.

Popular Window Styles

In the St.Louis Metro Area, choosing the right windows for you can be a hard choice! From freezing cold winters to hot summers, you need to be ready for all weather conditions to keep internal temperatures comfortable.

In this day and age, the number of window options can seem endless. Here at XteriorPRO / Window Depot of St. Louis, we specialize in the most popular window styles in our area while staying up to date on the newest hottest trends in home design.

Our XteriorPRO / Window Depot of St. Louis staff is highly trained in installing the following types of home windows:

  • Double-Hung Windows: The most popular window style in the United States.
  • Casement Windows: Single unobstructed glass window pane with the option of opening with a hand crank.
  • Awning Windows: Unique hinged sash that opens into the home, allowing the window to be open during a rainstorm without bringing water into the home.
  • Bay & Bow Windows: Typically have a large window sill perfect for sitting and watching the birds. They also open outward to let in a fresh breeze.
  • Garden Windows: Garden windows also have a large window sill in a square or rectangle shape. These windows encase the extended window to allow sunlight in from the right side, left side, front, and from above.
  • Horizontal Slider Windows: These windows are wider than they are tall and are perfect for just about anywhere within the home, especially places you want a great view of nature.
  • Picture (Fixed & Speciality) Windows: Picture windows are fixed in place and do not open. These windows can be shaped to exact customer dimensions to suit that hard-to-decorate room.

Still Have Questions? Reach Out Today!

Hopefully, this comprehensive window terminology guide answered most of your questions and gave you a better idea of the intricacies behind one of the most common parts of a home.

If you have any questions about the window installation process or the materials we use, give us a call at (636) 939-4800.

We have been faithfully serving St. Louis, St. Charles, and Jefferson County residents for years now and are honored to serve for many more to come.