It's Writing.com lingo for different ways you store work in your portfolio.

This is an "item": "Nimue" 

You use the code {item:xxxxxx} to display an item.

This is an "entry": "Chapter 1" 

You use the code {entry:xxxxx} to display an entry.

An entry is always inside of a larger item (specifically, a "book" item.)

Cheers,
Michelle