Day-age creationism, a type of old Earth creationism, is an interpretation of the creation accounts in Genesis. It holds that the six days referred to in the Genesis account of creation are not ordinary 24-hour days, but are much longer periods (of thousands or millions of years). The Genesis account is then reconciled with the age of the Earth. Proponents of the day-age theory can be found among both theistic evolutionists, who accept the scientific consensus on evolution, and progressive creationists, who reject it. The theories are said to be built on the understanding that the Hebrew word yom is used to refer to a time period, with a beginning and an end and not necessarily that of a 24-hour day.
The differences between the young Earth interpretation of Genesis and modern scientific theories such as Big Bang, abiogenesis, and common descent are significant. The young Earth interpretation says that everything in the universe and on Earth was created in six 24-hour days, estimated to have occurred some 6,000 years ago. Modern scientific observations, however, put the age of the universe at 13.7 billion years and the Earth at 4.6 billion years, with various forms of life, including humans, being formed gradually over time.
The day-age theory tries to reconcile these views by believing that the creation "days" were not ordinary 24-hour days, but actually lasted for long periods of timeāor as the theory's name implies: the "days" each lasted an age. According to this view, the sequence and duration of the creation "days" is representative or symbolic of the sequence and duration of events that scientists theorize to have happened.
Read more about Day-age Creationism: History, Interpretation of Genesis