To best illustrate what an item is in practice, let us go over the lifecycle of each of the many items you learn in HanziHero.
Once you successfully complete the lesson for an item, it becomes a new item. A new item is an item you have just learned but may not be sufficiently familiar with yet.
Once you learn an item, it will begin to show up in your reviews. If you successfully review an item multiple times in a row with no mistakes, it will become a familiar item. A familiar item is something you know well enough that you can probably recognize it without too much difficulty, provided you saw it recently.
Some items have other items they are dependent on. These are called dependent items. These dependent items must be familiar first before we can learn the items themselves.
For example, a character will have all sound and component items that it contains within it be considered its dependent items. Only when you are familiar with all of the dependent items for an item will the item start to show up in your lessons.
As you review items, their SRS stage will move up or down according to how many tries it took to answer their questions correctly in your reviews.
When an item reaches the final SRS stage, it will become a finished item. Finished items will no longer show up in your reviews, as they represent information that you have already truly memorized!