The term heptad comes from the Greek word for "seven" and is used to refer to groups or series of seven in various contexts. In the context of the Biblical book of Revelation, heptads refer to several sets of seven that are significant in the symbolism and structure of the text. These include:

Seven Churches: Revelation chapters 2 and 3 mention seven churches in Asia Minor (modern-day Turkey). These are Ephesus, Smyrna, Pergamum, Thyatira, Sardis, Philadelphia, and Laodicea. Each church receives a specific message.

Seven Seals: In Revelation 6 and 8, seven seals are opened by the Lamb (Jesus Christ), each unleashing a different event or series of events on Earth. The opening of the seventh seal leads to the introduction of the seven trumpets.

Seven Trumpets: These are found in Revelation 8, 9, and 11. The blowing of each trumpet signals the coming of a new judgment or plague upon the earth.

Seven Bowls (or Vials): These are described in Revelation 16, where seven angels pour out bowls containing God's wrath, resulting in various disasters and plagues.