A Shop is a project where a Scratcher can get resources (like sprites or scripts) sometimes, but rarely, on request. They can be very useful, for example, if one wanted to make make a game with fish, but did not know how to draw them, they could find an "Ocean" sprite pack. The resources are usually used through the backpack.
An example shop.

Sprite Packs

These are probably the most common type of shop. They are projects with sprites for other Scratchers to use. Sometimes shops will contain a specific type of sprites for others to use, such as animals or fantasy objects. Rarely, Scratchers can request specific sprites.

Sound/Song Shops

A sound shop is a project with sounds and music for other Scratchers to use. These kinds of shops are quite rare.[problematic] A song shop is a project with songs, either as sounds or as scripts with the note-related blocks in the Sound category. They are probably the most common type of sound shop. Sometimes Scratchers will use songs from popular artists around the world, and put them in these kinds of shops.

Voice Acting Shops

Main article: Voice Acting

A Voice Acting shop is a sound shop with voices, where Scratchers can request voice actors for a project they might be making.

Scripts

A script shop is a project with scripts to use in a project. These are useful when you do not know how to make a script do something, such as make a cloud list.

Custom Block Shops

One of the most common type of script shops is a custom block shop, where Scratchers create Custom Blocks for others to use.

Idea Shops

Main article: Idea Shop

An Idea Shop is a shop where Scratchers can get ideas for projects.

Art Shops

These shops are similar to sprite shops but they create logos, banners and other art that can be used on the scratch website.

"Everything" Shops

"Everything" shops have many different products, such as art, music, and scripts. These are not quite as common.