The namespace identifies where the application will have read and write access. It's similar to what a "folder" is in operating systems. All operating systems have a root user folder in which users can read and write data. Usually that folder has many subfolders, created by the operating system, such as Images, Music, Videos, Documents, Downloads etc. Similarly, namespace is the root folder for the application. The application has read and write access and is able to structure the data in subfolders.
Namespace is integral to HAT applications as every application is required to specify one upon creation. During the application creation process the application is given read and write permissions to the specified namespace. This allows the application developer to structure the data in a way that meets the particular business needs of the application. It also ensures data integrity in the HAT ecosystem. This integrity is maintained as applications read and write data into their own namespace therefore eliminating the possibility of duplicates and enforcing applications to only write to their own namespace.
Please note that currently it is not possible to change the namespace once the application has been created.