Japanese Cucumbers is just an English-language generalization for cucumbers grown in Japan. Obviously, there’s more than one type of cucumber grown in Japan.
Varieties classed by English speakers as Japanese cucumbers include Kyoto, Palace King, Soarer, Sooyow Nishiki, Suhyo, Tasty Green, and Tsuyataro.
The cucumbers are long, narrow and have thin skin. They tend to look like English cucumbers, only they are less smooth, having a few bumps on them, and sometimes prickly skin. They have small seeds. And, like English cucumbers, they tend to be burpless.
There is no need to seed or peel them (if the skin is not prickly.)
Cucumbers are often used in cooking in Japan.