A more thorough explanation:

An Article III judge is a judge who serves on the U.S. Supreme Court, Court of Appeals, or District Court and is appointed for life under Article III of the U.S. Constitution.

For example, Justice Ruth Bader Ginsburg was an Article III judge who served on the U.S. Supreme Court from 1993 until her death in 2020. Judge Merrick Garland is an Article III judge who currently serves on the U.S. Court of Appeals for the District of Columbia Circuit.

These examples illustrate the definition of an Article III judge because they both served or currently serve on a federal court that is established under Article III of the U.S. Constitution. They were appointed by the President and confirmed by the Senate, and they hold their positions for life unless they resign, retire, or are impeached and removed from office.