Musiker's major field of study, listed on her personnel file
A major was an academic field of study that an individual concentrated on.
Tom Paris majored in astrophysics at Starfleet Academy, a fact he divulged to Rain Robinson in 1996 when she expressed her surprise that he was smarter than she believed him to be. (VOY: "Future's End")
In 2151, Daniels apologized to Jonathan Archer for the mess in his quarters, saying sometimes he believed his bunkmate majored in chaos theory. (ENT: "Cold Front")
In the 24th century, Devinoni Ral focused on interstellar law at the Oneamisu Campus of the University of Hurkos before switching his major to political science. (TNG: "The Price")
In the 2340s, Data majored in probability mechanics at Starfleet Academy. (TNG: "Conundrum")
In the 2370s, Raffaela Musiker majored in intelligence at Starfleet Academy, where she minored in Romulan Relations. (PIC: "The Next Generation")