The days of the week, the Harry Potter books, the notes in a normal major or minor scale, the games in Major League Baseball postseason series, and the Pillars of the House of Wisdom in the Book of Proverbs are some examples of things that appear in groups of seven.
The number of heavens in Islam and the chakras in Hinduism are two further examples of groups of seven.
The number of official measurements in the International System of Units, the number of the Big Dipper’s main stars, the cervical vertebrae of most mammals, the periods on the periodic table of elements, and Newton’s seven rainbow colours are just a few examples of groups of seven that can be found in science.
The number of blessings at a Jewish wedding, the levels of the Earth in Islam, the seven planets in the universe according to Hinduism, the Seven Sorrows and the Seven Joys of the Virgin Mary, and Jesus’ final words spoken while hanging on the cross are all examples of religious groups of seven. The creation account in the Old Testament mentions seven days.
The seven seas, the seven continents, the seven hills of Rome and Istanbul, and the seven Greek sages are examples of groups of seven in the classical world.