Biblical literalism is the belief that the Bible, or at least large portions of it, should be read literally, not allegorically.
To some extent, literalism is a matter of degree, since not even self-described literalists claim to believe that everything in the Bible is literal. For instance, Isaiah 40:22 says,
- He sits enthroned above the circle of the earth, and its people are like grasshoppers. He stretches out the heavens like a canopy, and spreads them out like a tent to live in.
No one believes that this passage means that humans are green and have six legs.
However, literalists do believe that unless there is good reason to suppose otherwise, the Bible is to be taken literally: Genesis and the Gospels are historical documents; Adam and Eve were real human beings, not metaphors, there really was a worldwide flood, and it is a statement of historical fact that Jesus was crucified and rose from the dead.
Literalism vs. science
Since a literal interpretation of the Bible makes many verifiable claims, it is the easiest to disprove. For instance, if there really had been a worldwide flood, there should be a recent worldwide layer of silt in the geologic column. This is not the case. Also, a literal reading of Genesis would lead to a belief in Young-Earth creationism (YEC). YEC states that the earth is less than 10,000 years old and is not compatible with the theory of evolution, which is widely accepting in scientific circles. A metaphorical/allegorical reading of Genesis would be necessary in order to make the creation account in Genesis align with modern scientific understanding.
Since it is similarly easy to disprove the literal truth of many biblical claims, it is not surprising that more educated theists tend to adhere to different, perhaps more sophisticated interpretations of the Bible. One charge often leveled at books such as Richard Dawkins's The God Delusion is that they miss the mark: while it is easy to disprove biblical literalism, no one believes it anymore. In other words, literalism is seen, even among theists, as crude, unsophisticated, and bad theology.