The City of Chicago (plaintiff) enacted an ordinance criminalizing “loitering” in a public place with one or more other people. The ordinance defined loitering as "remain[ing] in any one place with no apparent purpose." Under the ordinance, if a police officer observed someone the officer reasonably believed to be in a criminal street gang "loitering" in a public place with one or more other people, the officer could order the people to disperse. Anyone who did not follow the dispersal order would be in violation of the ordinance. Morales (defendant) was convicted under the ordinance. However, the state appellate court reversed his conviction. The Supreme Court of Illinois affirmed the appellate court's judgment, holding that the ordinance violated the Due Process Clause of the Fourteenth Amendment because it was impermissibly vague. The United States Supreme Court granted certiorari.