A resource bundle is a Java .properties file that contains locale-specific (language) data. It is a way of internationalizing a Java application by making the code locale-independent. (Source: Wikipedia)
Canvas provides an option to display plain label (i.e., direct text) or Display Name Key (i.e. property driven label text) for components. By default, Canvas uses the common properties file (e.g. common_en_US.properties) that contain the display names for the default Canvas components in the CT ModelHouse application, such as Workspaces, Sub-Workspaces, Apps, Views, Forms, Form Items etc. The resource bundle properties file contains the display text for the display name key specified in the configuration screens.
The resource bundle field is mandatory on the configuration screens in Canvas Studio. However, if you want to display plain text for the components and do not wish to use the resource bundle, you can enter ‘none’ for the resource bundle field.