A high-up is a person with a high rank — a boss, a director, someone near the top of a company, a school, or the government. It is informal corridor talk, not report talk. People say the high-ups to mean “the people in charge,” often with a little distance or a small complaint: the high-ups decided; the high-ups will not like this. Though actually, in careful writing you would say senior managers or executives. You may also hear a high-up in the firm / in the party. Do not mix this noun with high up as two words, which often just means “in a high place.”

高層；上頭的人（口語）