Gap creationism (also known as ruin-restoration creationism, restoration creationism, or "the Gap Theory") is a form of old Earth creationism that posits that the six-yom creation period, as described in the Book of Genesis, involved six literal 24-hour days (light being "day" and dark "night" as God specified), but that there was a gap of time between two distinct creations in the first and the second verses of Genesis, which the theory states explains many scientific observations, including the age of the Earth.[1][2][3] It differs from day-age creationism, which posits that the 'days' of creation were much longer periods (of thousands or millions of years), and from young Earth creationism, which although it agrees concerning the six literal 24-hour days of creation, does not posit any gap of time.
^Evolution vs. Creationism: An Introduction, Eugenie Scott, pp61-62
^The Scientific Case Against Scientific Creationism, Jon P. Alston, p24