The way you define the kind of content you can edit inside your administrative area passes through the concept of Models, which are much like database tables. For backward-compatibility reasons, the API refers to models as "item types".
Name of the model
API key of the model
Whether the model is single-instance or not
Whether editors can sort records via drag & drop or not
Whether this model is a modular content block or not
Whether editors can organize records in a tree or not
If an ordering field is set, this fields specify the sorting direction
Specifies the model's sorting method. Cannot be set in concurrency with ordering_field
Whether draft/published mode is active or not
Whether we require all the project locales to be present for each localized field or not
The way the model collection should be presented to the editors
If this model is single-instance, this tells the single-instance record has already been created or not
A hint shown to editors to help them understand the purpose of this model/block
The item instance related to this item type
The list of item type fields
The field to use as display title
The field upon which the collection is sorted
The workflow to enforce on records