Associate justice is the designation given to a justice on a judicial panel who is not the chief justice.
Most commonly, the term is used to describe one of the eight associate justices on the Supreme Court of the United States, although many state courts of last resort also designate the judges on their judicial panels as “chief justice” and “associate justices.”
An associate justice on the Supreme Court of the United States is appointed by the President and confirmed by the Senate; once confirmed, s/he has life tenure and can only be removed by impeachment or voluntary retirement.
The eight current (as of June 1, 2021) associate justices of the Supreme Court of the United States are (in order of seniority): Clarence Thomas, Stephen Breyer, Samuel Alito, Sonia Sotomayor, Elena Kagan, Neil Gorsuch, Brett Kavanaugh, and Amy Coney Barrett.
[Last updated in June of 2021 by the Wex Definitions Team]