In MATLAB, NaN stands for "Not-a-Number". It is a special value used to represent undefined or unrepresentable numerical values, such as the result of mathematical operations that do not have a well-defined value or operations that produce a complex number when only real numbers are expected. NaN is commonly used to indicate missing or undefined data in numerical arrays. For example, if a particular element in an array cannot be computed, it can be assigned a NaN value to indicate that it is missing. NaN values can also arise when dividing by zero or taking the square root of a negative number. To set a new variable as NaN simply use: variable = NaN;