About User-Defined Custom Dimensions
You can add up to 13 user-defined custom dimensions. For example, you could add a dimension called Project to budget operating expenses for each project. You define properties, including name, alias, plan type, security, attributes, and attribute values.
Caution:
You cannot delete custom dimensions after you create them.
User-defined custom dimensions differ from the Entity and Account dimensions in that you assign valid plan types at the dimension level, not at the member level. All members of a user-defined custom dimension are valid for plan types assigned at the dimension level.