高等 (gāo děng) is a formal adjective used in fixed terms for a higher stage of education, math, or biology (e.g., 高等教育, 高等数学, 高等动物). Unlike 高级 (gāo jí, 'high-class/senior'), which indicates quality or rank, 高等 specifically marks a level in a graded system. It also differs from 先进 (xiān jìn, 'advanced/progressive'), which focuses on being ahead in technology or ideas.