Ideas can be both concrete suggestions as well as more vague thoughts about how clients would like the product/outcome of the project (whereas issues represent problems that need to be fixed).
An idea is in many ways the same as a story: it has many of the same properties and can be planned and handled like a story. It can even be converted into a story.
However, ideas can also be set as implemented by a story. The state of the idea will then follow the state of the story.
Ideas are placed along with issues in a separate part of the Storymap Tree and can be categories in folders.