A pianist's skill in manipulating volume is often referred to as "touch" or "technique." Pianists with strong technique are able to play notes clearly and use dynamics to accentuate their performances.
The piano is a very versatile instrument that can be used in a number of different genres. Classically trained pianists will learn the importance of both technique and touch to make their playing more beautiful, dynamic and emotional.
Technique refers to the actual physical motion and positioning of a player's body, specifically the fingers, hands, wrists and arms. Correct technique will not only prevent strain and injury, but will in fact help a player to play more quickly, clearly and efficiently. It will also help players manipulate the volume at which they are playing without compromising their sound or clarity.
Touch more refers to the nuances that players add to their own performance. Some players always play too loud, while other always play too soft. A player with great touch will be able to seamlessly transition from loud, fortissimo parts to softer, pianissimo passages. Touch brings "life" to a song, and it allows players to add their own personality and emotions into their playing for the listener to enjoy.