A pre-law degree is any degree which would allow someone to enroll for law school. All ABA law schools require at least a bachelors degree for North American students. Therefore, it is not a major, but any set of courses within any bachelors degree program (whether required as part of a major or elective) which prepare one for law school.
Pre-law students may be advised or required to take upper level political science and sociology electives, such as legal systems, criminal law, international law, Policy, etc. Specific requirements for these courses vary by institution.