In their owners' manuals, some automakers may make a distinction between minor and major tune-ups when it comes to auto maintenance. In general, a minor tune-up is usually performed every 30,000 miles, while a major tune-up will be saved for the 60,000 or 90,000 marks. There are some significant differences between the services that are usually included in each of these terms.
A minor tune-up usually focuses on the fluids. It's a good idea to check all fluid levels and top off anything that looks to be getting a little low - this includes power steering, transmission, brake and radiator fluid. On the electrical side of things, it might be a good idea to replace spark plugs during a minor tune-up as well. If it's been a few thousand miles since your last one, an oil change could be included in a minor tune-up as well.
Major tune-ups are a bit more labor intensive. Besides just looking at the spark plugs in the electrical system, a major tune-up will also replace the spark plug wires, distributor cap, rotor, and points and condenser. The fuel filter will likely need to be replaced as well. Obviously, all fluids will be topped off as in the minor tune-up, but you should also inspect the rear-differential oil and any oil needed for a manual transmission. This is also a good time to add antifreeze and look at the windshield wiper fluid.
Optionally, be sure to check out your brake pads and tires as well, as these also need to replaced from time to time. Even if your tires do not need to be replaced, a major tune-up is a good time to rotate them or fill them up with more air.
Essentially, there is no strict definition for what exactly a tune-up entails. Some drivers will prefer to do everything all at once and call it a tune-up, even if it winds up taking them a few hours. In that same vein, some quick-lube shops might include services in their tune-up packages that others do not. In general, the most important thing to remember is that all of these systems need to be inspected and double-checked from time to time to ensure that everything is working properly. If you keep up with your maintenance in this fashion, you can avoid making expensive repairs down the line.