Final answer:
Sitecore supports Data Definition with Data Templates, which define the structure of data. Items are instances of these templates, representing individual pieces of content. This provides consistency and flexibility in content management.
Step-by-step explanation:
Sitecore supports the CMS pillar Data Definition through the use of Data Templates. Data Templates in Sitecore serve as the schema for the content managed in the CMS. They define the structure of data by specifying what fields are present and the types of data each field can contain. Essentially, they are the blueprints that determine how data is to be structured and stored.
Within Sitecore, items are instances of these Data Templates. Each item represents a piece of content which inherits the fields and data types outlined in the Data Template it is associated with. This enables Sitecore to manage a wide variety of content with consistency and flexibility, allowing content creators to focus on providing high-quality and structured content without worrying about the underlying data design.