a washer is generally a rubber washer that tightens and seals as sometimes they will go bad and have to change it..
Proably the faucet has a worn out washer, replacing the washer should fix the problem.
It fills the washer with water from the source, Theres usually a cut-of valve or faucet on the wall near the washer for it.
Washer worn out, washer seat damaged/corroded The most likely reason is that the sealing washer or seat in the tap/faucet is defective.
more flow but do not last as long as beveled ===
When you shut the faucet off, the screw pushes a rubber washer against the opening inside the faucet and stops the water. The screw moves in and out in the handle to do this.
A power washer should be connected to a garden faucet.
You remove the handle then unscrew main interior body of the faucet. You will now see a small screw on the inner end of the stem holding the washer. Remove this screw and refit the same size washer (there are dozens of sizes, you may have to get an assorted bag of washer from the store, -only about $3-4)
Loose washer
This is just a guess. If only the hot or the cold stops and not both of them, it might be that the washer in the shut off valve has come off and is plugging the line. When you shut off the main and then open another faucet, the back pressure in the line pushes the washer out. If this is the case, the washer should still be in the shut off valve. Turn off the main and take the stem out of the faucet. The washer should be the valve.
The rubber stop washer has failed.
Depends on the condition of the seat of course
You take the faucet apart and replace the washer and stem seal .