The definition for a "classic" car differs depending on if you are getting the definition from a car club, insurance company or your state department of motor vehicles.
The Classic Car Club of America (CCCA) has a list of cars that are recognized qualifiers as classic. The CCCA's definition of classic refers to cars made between 1925 and 1948, however there are many exceptions to this long list. The list is very specific as to what makes of each model are given the "classic" designation.
Most insurance companies consider your car an antique or classic if it is at least 15 or 20 years old or older (depending on where you live), garaged when not in use, and driven less than a set amount of miles (generally less than 2,500 miles per year but some insurance company gives up to 5,000 miles/year).
Many insurance companies also require that you own at least one other vehicle for "regular" use. Regarding the insurance itself, if you have more money in your car than what the blue book lists, you will need to get it appraised and get and get an "agreed value" insurance policy. It will cost you less than a standard policy, and more importantly, you'll get the true value of your car should it be damaged or totaled. Under agreed-value policy terms, the insurance company and the vehicle owner discuss the value of the vehicle --and agree on it -- so that it is covered up to that dollar amount in the policy.
To learn about insuring a classic car, check out our guide to insuring classic cars.
The department of motor vehicles (DMV) definition for a classic car differs from state to state. In general, though a classic is any vehicle older than 15 years while an antique is more than 25 years old.
To find out your state's definition of a classic car and how old it must be to be considered a classic or antique check with your state's DMV.