student council president; head of the student council
Refers to the elected leader of a school's student council. Common in junior high and high school contexts.
He ran for student council president.
As student council president, I want to improve the school rules.
Refers to the student council itself, not the person leading it.
A general term for president or chairperson of an organization; 生徒会長 specifies the student council context.
Compound of 生徒 (student), 会 (council/association), and 長 (leader/head).