It is the Aquapik cordless oral irrigator.

It is the Aquapik cordless oral irrigator.
There may be people who have never used it, but there are no people who have used it only once.
I think this is probably the most representative example of that expression.
It is an oral irrigator called a water flosser. It is a device that removes debris stuck between the teeth and gums by spraying a strong stream of water. It is generally said to be effective in inhibiting dental plaque, preventing cavities, and improving gum health.
You are probably well aware that managing the 'periodontal pocket,' where foreign substances easily get trapped between the teeth and gums, is important.
They say the periodontal pocket is the very source where bacteria multiply.
I think it's the best for removing debris from periodontal pockets that isn't easily removed by brushing.
Instead, since its purpose is to remove relatively large chunks of food debris that may be stuck between teeth, not to clean the spaces between them thoroughly, it is recommended to use an interdental brush as well.
Cordless products are also useful when traveling.