A faucet cartridge is a valve that turns your faucet off and on and mixes the hot water with the cold. It is often below the handle. Cartridges can plug up over time which can cause either a leak at the body of the faucet or a constant drip.
If a cartridge is plugged on a newer faucet it is often because the water line was not flushed before the faucet is installed. When a sink is remodeled the sink and faucet are removed. This work can often knock loose deposits that have built up over time in the pipes. By flushing the lines prior to installing the new faucet you clear the line of debris and the cartridge will function properly. If the lines are not flushed the cartridge and even sometimes the aerator will plug a impact the performance of the faucet or cause a leak.
The cartridge can also become blocked with a buildup of minerals from very hard water.
Replacing the cartridge is relatively easy. The Eclipse “repair kit” comes with most of the tools you will need, all the “O” rings and a new aerator. Here are pictures of the cartridge replacement process. Make sure you turn off the water at the wall before replacing the cartridge.