A magic number is a hard-coded numerical value that may lack context or meaning. They should not be used because they can make the code less readable and maintainable.

== Why is this an issue?

Magic numbers make the code more complex to understand as it requires the reader to have knowledge about the global context to understand the number itself.
Their usage may seem obvious when writing the code, but it may not be the case for another developer or later once the context faded away.
-1, 0, and 1 are not considered magic numbers.