What is the solvent and what is the solute?
In a binary homogeneous mixture, the component present in the larger amount is generally called the "solvent". The component present in the smaller amount is generally the "solute".

In your first example, however, it is more complicated as coffee is already a complex solution (but mainly water). Milk is not a homogeneous mixture. It is a fat/protein emulsion (also mainly water). 

The other three are solutions: salt water is a solution of a solid dissolved in a liquid (which is the most familiar type), air freshener (one dispersed) is a solution of one gas in others (but air itself is a mixture), and brass is a solid solution.