The word "dimensional" describes a design method. The word "relational" describes a data storage technology.
- A dimensional model is a design approach that describes a process in terms of measurements (known as facts) and their context (dimensions)
- A star schema is a dimensional model implemented using relational storage technology—that is, in a relational database (RDBMS)
- A cube is a dimensional model implemented using multi-dimensional storage technology—that is, in a multidimensional database (MDB)
By the way, don't let this confuse you: most modern day DBMS products accommodate both kinds of storage.