Shopping for new windows shouldn’t feel like learning a foreign language. But if you’ve heard terms like sash, mullion, or glazing and thought, “Is this a window or a medieval structure?” — don’t worry. You’re not alone.

Let’s clear things up. I’ll walk you through the most common window terms using a couple of examples from the shop, so next time someone throws around “double-hung” or “jamb,” you’ll actually know what they’re talking about.

The Frame: The Backbone of the Window

Let’s start with the obvious: the frame. It’s the outer part of the window that gets installed into the opening in your wall. Everything else fits into or around this.

Here’s how it breaks down:

Jambs are the vertical sides of the frame.
Header is the top part.
Sill is the bottom ledge the window sits on.

Think of the frame like the window’s skeleton — it holds the structure together and locks it into place.

Double-Hung Doesn’t Mean Twice the Headache

If someone tells you the window is “double-hung,” It simply means that both the top and bottom sections (called sashes) can move up and down.

You can slide the bottom sash up or the top sash down. This gives you better ventilation, more flexibility, and makes cleaning way easier.

The Sash: Not Just a Fancy Word

The sash is the part of the window that holds the actual glass. It frames the pane of glass and allows it to move.

Without the sash, the glass would just be floating there — which sounds cool, but definitely wouldn’t pass inspection.

Some windows come with decorative grids across the glass, giving them a classic, divided-pane look. Others go grid-free for a clean, modern appearance.

It’s all about style and preference. You can also get extras, like built-in blinds between the glass panes. These let you control light and privacy without needing external blinds or shades — and without ever dusting again.

Glazing = Glass (And Yes, It Matters)

Here’s where it gets a little technical but still easy to understand.

Glazing is just another word for the glass in a window. You’ll also hear the word “pane,” and in most cases, they’re used interchangeably.

When someone says a window is “double-glazed,” it means there are two panes of glass. “Triple-glazed” means three.

More panes mean better insulation, more energy efficiency, and even a quieter home. So yes, those extra layers are doing more than just sitting there looking clear.

Locks

Modern windows come with several types of locks for safety, insulation, and ease of use. Here are the main ones you’ll come across:

Anti-theft stops: These are small latches at the top that you can flip out. They prevent the window from opening past a certain point, adding a little extra peace of mind.
Sash lock: This is the primary lock that keeps both sashes tightly closed.
Tilt latches: These let you tilt the sashes inward so you can clean the outside of the glass from inside your home.

Being able to clean your windows without climbing a ladder? Huge win.

Cleaning Tip: Don’t Let Your Window Go Crooked

When you tilt a window inward to clean it, you’ll notice little pivot pins on either side of the sash. These fit into tracks called slider blocks.

Before you push the window back into place, make sure both pins are properly seated in the slider blocks. If one side is off, the sash will sit crooked and won’t close or lock properly.

If it feels uneven, don’t force it. Just double-check both pins and reset if needed.

Mullions: The Dividers of Big Glass

If you’re looking at a big window — like a bay window — you might see vertical bars breaking up the glass into sections. These are called mullions.

They’re not just for looks. Mullions help support large panes of glass and add structural stability, especially in wider or taller window openings.

So while it may look like three windows side by side, it’s really one big window with built-in reinforcements.

The dividers of smaller windows are called Grids or Muntins. Historically these kept the glass within the window, but nowadays they are used for aesthetics and are usually purely decorative

Final Thoughts: You Know Your Sashes from Your Sills

Now that you know your glazing from your grids and your mullions from your jambs, the world of windows should feel a whole lot less confusing.

Whether you’re replacing one window or designing your dream home, understanding these terms can help you ask the right questions, spot quality features, and make smarter decisions.

And if you still need a hand, we’re always here to make the process simple — and maybe even a little fun.