Captions allow you to change the displayed text of a dimension.
Ie : If you have a client_id and client_name dimensions, you can choose to display the client_name when you use the client_id in a graph

Captions from the same data model

• The data model contains the id and the caption of the dimension
  • Example : ID Client in the database and its common name

Click on the dimension (ID Client in the example) that must have a caption
In the caption option, choose the column to display

Caption from external data model

• “star type” modelisation. The data model contains the id (fact table) and another data model contains the ID and the associated caption