Grands are now simply classified by size. This depends very much on the make of piano, the type of piano, its age, general condition, and so on. For a more detailed discussion of this subject please read the piano valuation page . This is a matter of personal taste. There are two extremes.
Most domestic pianos require tuning every six months.
It is the setting up of each part of a piano action so that it does exactly what it should. A regulated piano has a uniformly graduated touch response and tone throughout its compass. See the Grand Piano Regulation Page for details on how it is done. When a key is pressed the action of the piano transfers the momentum of the moving key to a felt hammer which is launched towards the strings for that particular note. The hammer strikes the strings and bounces off leaving the strings to vibrate.