Plasma physics was a branch of physics and one of the oldest Federation academic disciplines. It was an experimental science and used the scientific method to formulate and test hypotheses. The theoretical branch was termed plasma dynamics.
From the 21st century on, plasma physics was used in the invention, and subsequent development of warp drive. Federation warp technology used plasma to create warp fields. Additional Federation ship systems used plasma in EPS conduits throughout.
Plasma physics had two main branches of application. Those who specialize in experimental investigations were known as plasma specialists. In 2368, Robin Lefler told Wesley Crusher about her parents who were both plasma specialists. The experimental nature of their work was described by her time growing up "all around technical equipment." (TNG: "The Game")
Plasma physics was a course of study at Starfleet Academy. This course taught both theoretical analysis and experimental investigation. Wesley Crusher was conducting a plasma physics experiment aboard the USS Enterprise-D which he used in a wargame. (TNG: "Peak Performance").