AOL

Baffled by obscure car terms? Learn to speak the language of the motoring tradesman.

1. Book price
The value of a car based on the monthly price guides to which the trade refers.

2. Diff
Short for 'differential'. This is a device that lets a car's wheels turn at different speeds, allowing it to go round corners smoothly.

3. Diff lock
Device used on some off-road vehicles. It stops the wheels spinning when you don't want them to, by locking up the differential.

4. Full-time four-wheel drive
System used on all 4x4 cars and many off-roaders by which the engine drives all four wheels at all times.

5. Heap
Broken-down old wreck.

6. Log book
Commonly used name for a vehicle's registration document. Every car should have one, so remember this when buying or selling.

7. Low range
Off-road vehicles have two sets of gears. High range is for normal driving; low range is for off-roading at low speed.

8. MoT
Annual test for cars aged three years and over, required by law to ensure the vehicle is in a safe condition.

9. Registration document
Official form (V5) issued by the DVLA for every car, containing essential details on the vehicle and its owner. If you own the car, you should have this.

10. Road tax
Vehicle Excise Duty, to give it its proper name, or the tax you pay to use public roads. Once paid you get a paper disc to display on your windscreen.

11. Service record
A booklet that comes with a new car. Every time the car is serviced, the garage puts its stamp in the book - so long as the correct service schedule is maintained.

12. SORN
Statutory Off-Road Notification. If you own a car but don't want to tax it because you're not using it on the road, you must send in a SORN form. This costs nothing.

13. Tread
When you look at the surface of a tyre it's not smooth - it has a pattern of raised 'blocks'. These are the tread and it is crucial to determining how the tyre performs.

14. Warranty
A document you may get with a car that makes a set of promises regarding its condition. New cars have a three-year warranty; with used cars, it's more likely to be six months. Under the terms of the warranty, it's up to the seller to put problems right.

15. Wedged
Charming motor industry term: if you have a car 'wedged', it means you're finding it hard to sell. The origins of this phrase are best left to the imagination.