Definition: A state in which a computer programmer has no success in conceiving ideas or logical structure when writing a computer program, regardless of their actual experience or ability with the subject.
Layman's Definition: No matter how hard a programmer tries, they cannot come up with any coding ideas. They can sit at the computer for hours (and days) unable to think of any code to write.
This state can last for a variable length of time and has many external factors which play a role (i.e. stress and current mental state).
Compare with Writer's Block.
The inverse of Code Block is Code Run.