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The Complete Glossary of Internal Door Terminology
Understanding the terminology used in the internal door industry can be confusing—especially when you’re choosing new internal doors, comparing door types, or arranging a professional supply and fit service. To help, we’ve created the complete glossary of internal door terminology, covering every essential term you’ll come across when buying, measuring, or fitting internal doors.
Whether you’re upgrading to modern oak internal doors, choosing fire-rated FD30 doors, selecting new door hardware, or working with our expert joiners in Leeds and West Yorkshire, this glossary will help you understand exactly what everything means.
A–C: Essential Internal Door Terms
Architrave
A decorative moulding fitted around the outside of a door frame. Architrave covers gaps between the wall and the frame and provides a neat, finished look.
Bi-Fold Door
A door that folds in the centre using a track and pivot system, commonly used for cupboards, wardrobes and small openings.
Bottom Rail
The lower horizontal section of a door, found on panelled or solid timber doors.
Casing (Door Casing)
Also known as the door frame or lining. This is the structure that supports the door and hinges. Casings can be adjustable for different wall thicknesses.
Clear Opening Width
The usable width of a doorway when the door is fully open. Important for accessibility and building regulations.
D–F: Door Construction & Fitting Terms
Door Blank
A solid, unfinished slab used for custom door designs or to create fire doors.
Door Lining
A type of door frame usually supplied flat-pack. Often used for internal doors in new builds or renovations. Can be trimmed for the perfect fit.
Door Stop
The thin piece of timber attached to the door frame that the door closes against. Helps with draught proofing and provides the final closing point.
FD30 / FD60 Fire Door
Fire-rated internal doors designed to provide 30 or 60 minutes of fire resistance. Essential in certain properties and must be fitted with correct fire-rated hinges, intumescent strips and hardware.
Face Veneer
A thin outer layer of wood (such as oak, walnut or ash) applied to the door surface. This provides a premium look without the cost of solid timber.
Flush Door
A smooth, flat door with no panels. Popular for modern and minimalist interiors.
G–L: Materials & Door Part Terminology
Glazed Door / Glazing
Internal doors with glass panels to allow natural light through. Available with clear, frosted or decorative glazing. Fire-rated glazing is also available for FD30 doors.
Grooves
Decorative lines or channels machined into the surface of a door. Many LPD internal doors feature V-grooves for a contemporary look.
Hinges (Butt Hinges / Fire-Rated Hinges)
The hardware that attaches the door to the frame. Fire doors must use fire-rated hinges—usually three per door.
Intumescent Strip
A heat-reactive strip fitted around fire doors. Expands when exposed to heat to block smoke and flames.
Latch
The internal mechanism that allows the door to close securely when the handle is turned.
Light
A glazed panel within an internal door.
M–P: Measuring & Installation Language
Margin / Gap
The space between the door edge and the frame. Standard internal doors require 2–3mm margins on each side. Incorrect margins lead to poor performance.
Measurement Service
A professional pre-order measurement provided by The Door Line to ensure the correct door size is ordered. Prevents fitting issues and costly mistakes.
Mortice Lock
A lock fitted inside the door rather than on the surface. Used mainly for bathroom doors or bedroom privacy locks.
Panel Door
A door with raised or recessed panels. Traditional and popular for period homes.
Pre-Finished Door
A door that comes fully factory-finished and ready to install. No varnishing or painting required.
Primed Door
A door that has been factory-primed and is ready for painting.
Q–S: Fire Safety, Structure & Aesthetic Terms
Rebated Door (Pair Maker)
A pair of double doors that overlap in the centre to create a tight seal. Often used in wide openings.
Routering
A process used to cut grooves into a door edge, often needed when fitting hinges, latches, or intumescent strips.
Satin / Chrome / Matt Black Hardware
Surface finishes for handles, hinges and latches. Matt black hardware has become a leading trend for contemporary internal doors.
Solid Core Door
A heavyweight, premium internal door with a solid construction. Offers superior sound insulation and durability, commonly used in homes and apartments.
T–Z: Finishing, Hardware & Specialist Terms
Threshold
The strip across the bottom of a doorway. Helps transition between different flooring types.
Trimming Allowance
The amount you can safely trim from the edges of a door without damaging its structure. Each LPD door model has its own trimming guidelines.
Unfinished Door
A door supplied without varnish, paint or stain. Ideal for custom finishes.
Veneer Match
Ensures consistency of colour and pattern across doors within the same range—important for matching multiple doors in the same property.
Warping
When a door twists or bends due to moisture or incorrect installation. Solid core doors and proper installation minimise this risk.
Why Understanding Door Terminology Matters
Knowing the correct terms helps homeowners:
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Choose the right internal doors for their home
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Understand fire safety requirements
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Compare door materials and construction types
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Select the best hardware and door accessories
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Communicate clearly with joiners and installers
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Avoid mistakes when ordering online
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Decide between DIY door fitting and a supply & fit service
For customers using The Door Line’s supply and fit service, this glossary helps you understand every step of the process—from measurement to installation.
Choosing the Right Doors With The Door Line
As Leeds-based specialists in internal doors, we offer:
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A full range of LPD internal doors
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Fire-rated FD30 and FD60 options
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Oak, walnut, white, glazed and modern designs
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Pre-order measurement service
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Professional supply & fit installation
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Expert joiners across Leeds & West Yorkshire
Whether you’re ordering a single door or renovating a whole house, we’re here to help you choose the perfect style with confidence.
