CROSSJOIN is used to return a table that contains the Cartesian product from the rows of another table. The same effect can be achieved by simply dragging the desired column into the rows and columns of a table visualization.
CROSSJOIN(table,table,[,table])
In the Power BI formula bar write:
crossjoin_tables = CROSSJOIN(BusinessTable,AdTable)
Cross Join the AdTable and BusinessTable
The demo shows crossjoin returning a table with both all rows from the Ad Source table and all rows from the Business Type table.