Anything that varies from the accepted norm or standard is called a deviation. It is common in math and science, but it can refer to anything that differs from the expected.
Deviation in nature is an important part of evolution. When something causes a creature’s DNA to change, it creates a deviation, or a changed characteristic. If the deviation makes the organism better able to survive, it passes the change on to its descendants. People are naturally given to change, so there are deviations in critical thought as well as in math and science. Those deviations often account for the creativity that gives rise to new ideas, or theories, or even musical styles.