A sectional refers to something that's divided into separate parts or sections. Think of a big sofa with different pieces attached together.
When people talk about a sectional, they usually mean a type of furniture like a couch or sofa that's made up of multiple connected parts. You'll often see them in living rooms or family rooms where there's plenty of space for everyone to sit comfortably. They're great for families because you can move the different sections around to fit your needs, and some sectionals even come with built-in storage like cupboards or shelves. If someone tells you they just bought a new sectional for their home, they might be talking about a big, comfy couch with multiple seats that they can rearrange as needed.
Relating to a section.
