“Core” courses may differ by college (e.g. is art or music “core”?).
How electives are viewed depends on what they are. Rigorous academic electives are more likely to be viewed favorably unless they displace expected base courses (e.g. if the student skips physics, foreign language level 3, and precalculus to take AP environmental science, AP human geography, and AP statistics, that may not look so good).