Almost all hardwood floors are sealed, even if the seal is just a coat of penetrating oil and a layer of paste wax. Sealing the wood protects the floor from moisture, which is the floor's worst enemy. Gentle cleaners are best for any hardwood floor finish, but oiled-and-waxed floors require a type of care you don't need to lavish on hard surface finishes. Use a simple test to determine what finish is on your floor.
Testing the Finish
A quick way to tell if your floor has a film finish or is simply coated with oil and wax is to run your finger along one of the boards. Smudging of the finish indicates wax, which is usually applied over penetrating oil, lacquer or shellac. Neither lacquer nor shellac are as common as they once were, but if the floor is older, you should test it by dabbing a board with rubbing alcohol. If the finish softens, it's shellac; if it doesn't soften, dab on a little lacquer thinner -- if that softens the finish, it's lacquer. Neither solvent has any effect on penetrating oil, varnish, polyurethane or polyacrylic finishes.
Removing Wax Buildup
Wax protects floors finished with oil, and some people apply it to lacquered and shellacked floors as well, although it can make these finishes dangerously slippery and isn't recommended. Because wax yellows with age, you have to periodically remove it and apply a fresh coat if you want the floor to look its best. Use a product intended for wax removal from hardwood floors for this -- not one intended for furniture. In a pinch, you can clean off old wax with mineral spirits, although you may need a bucketful of rags to do this; each rag will quickly become encrusted with old wax.
Cleaning and Rewaxing
Before applying a new coat of wax to an oil-finished floor, clean the wood with a commercial hardwood floor cleaner. These products don't contain water, so they won't damage the wood. You can also mop off old wax with ammonia and water -- mix 1/4 cup of ammonia with 1 gallon of water. Wring out the mop thoroughly each time you re-wet it, and mop with the wood grain. Rinse with clear water, and dry the floor with a rag before applying a new coat of wax. If you discover that the wax was covering a film finish, do not apply a new coat -- someone may have waxed the floor by mistake.
Maintaining a Film Finish
Polyurethane and polyacrylic finishes -- the most common ones -- need little care. Sweep occasionally to pick up loose dirt and "dust bunnies." Vacuum occasionally to get dirt out of cracks, using a soft attachment with no beater bar. When you mop the floor -- which you shouldn't have to do often -- use an ounce of dish detergent per gallon water, adding 1/2 cup of vinegar if you have to remove streaks or white salt deposits. Always wring out the mop well before using it, and dry the floor with a cloth to prevent damage from standing water.