Maintenance Coats (aka "Recoat")
Over time your floors take a beating. Children, although they may be the future, are at the present miniature human wrecking balls for your homes. Pets, great companions through thick and thin they may be, have little regards for the investment you put into your beautiful floors as they bulldoze their way from window to window doing perimeter checks on passerbys. Cleaned and sanitized dishes come with the price tag of the inevitable water drips in front of your sink and dish washer. All of these things slowly wear down the finish protecting your wood.
Luckily, there are recoats to help keep your floors protected with new finish. Recoats are a quick (generally 1-day) and cost-effective (a fraction of the cost of a full resand) way to help maintain your floors and get the most bang out of your flooring buck. The process is less intensive than a full sand (just a quick clean, some light abrading, and a new coat of finish is applied over the existing finish) but restores both the shine and protection of what your floors had when you first had them finished.
Full disclosure, there are limitations to what a recoat can accomplish so realistic expectations are needed. Deep scratches or areas where finish is already worn through (usually wood discoloration or brown-ish, gray-ish hazing is a dead giveaway) will most likely need more than a recoat to fix (the damage has already been done). Also, improper cleaning products (waxes, polishes, etc) can leave a film that can cause adhesion problems when trying to apply new finish so it is important to always use the right cleaners. Recoats can remove some imperfections, but they are defintely more "preventative maintenance" than "fix".
"How often do I need a recoat?!"
The recommendation from the National Wood Flooring Association and most finish manufacturers is every 3 to 5 years (see, it isn't just a sales pitch). A good rule of thumb is to watch high traffic areas such as entry ways (front and back doors) and kitchens (especially in front of sink, dishwasher, and fridge) to look for areas of sheen difference. Generally as finish wears down, the sheen of the finish will appear duller than the rest of the floor. It is possible to do isolated areas of recoating, although you run the risk of potentially having sheen variation between old finish and new in the interim, but usually within a month or two of wear and tear the sheens blend back together.