This definition of premillennialism from Wikipedia –
“Premillennialism, in Christian eschatology, is the belief that Jesus will physically return to the Earth (the Second Coming) before the Millennium, a literal thousand-year golden age of peace. The doctrine is called “premillennialism” because it holds that Jesus’ physical return to Earth will occur prior to the Millennium. [It] is based upon a literal interpretation of Revelation 20:1–6 in the New Testament, which describes Jesus’s reign in a period of a thousand years.”
This millennial view is just one view related to the end times of Bible prophecy. Other views include postmillennialism and amillennialism. However, it remains a prominent view among Christians. It dates back to the 2nd century with Justin Martyr and Irenaeus, bishop of Lyon.