The term "washi" comes originally from two words- "wa" meaning Japanese and "shi" meaning paper. Traditionally therefore washi is Japanese rice paper tape. It usually has a slightly translucent quality and a low-tack adhesive.
Washi tapes are so incredibly versatile. People use them in all kinds of craft projects and in journalling etc. I use them to seal my paper bag parcels as they are easily removed to open the package without leaving residue.
They are also great for:
*taping pictures or artwork to a wall
*wrapping around a plain tealight to pretty it up
*making little flags with cocktail sticks when folded over on themselves
*decorating notebooks, bookmarks or similar projects
*making greetings cards.
There are also rolls of individual washi stickers, like the hearts in the photo. These peel off one by one so are great for journalling.
Sometimes you will also find flat sheets of stickers listed on the website made in the same thin, translucent paper. These are called washi stickers and can be used in the same way as normal washi but covering larger areas. Typically they peel off a clear plastic sheet and are die cut.