Can I put items into folders?

Although I’m an Omeka newbie, I search topics that confuse me before I post question here. Today, I’m searching for the answer to “Can I put items into folders?” without much luck.

At first glance, it appears that items are displayed all in one list. What about applications that have multiple authors creating multiple sites each with hundreds or thousands of items? Is there any way to separate items into folders?

Assuming you mean on the administrative side (rather than the actual file structure), the conceptual equivalent of “folders” for organization would be item sets.