specialized subject; special subject
Refers to a subject or course of study that is part of one's major or area of specialization, typically in a university context.
At university, I have specialized subject classes three times a week.
He passed the exam for his specialized subject.
一般教養 refers to general education or liberal arts subjects, while 専門科目 refers to specialized subjects in one's major.
選択科目 is an elective subject, which may or may not be specialized; 専門科目 is specifically a subject in one's field of specialization.
Compound of 専門 (せんもん, 'specialty') and 科目 (かもく, 'subject').