Complexity of a code based on different complexity metrics.
* McCabe's complexity * Halstead complexity * Elshof complexity * Data complexity etc... Here is an example of complex code: https://github.com/sympy/sympy/blob/master/sympy/solvers/solvers.py
Complex programs are difficult to read and maintain. Reducing a code's complexity improves its organization.
How to fix this
Implementing simple methods, avoiding too many branches, avoiding too much multilevel inheritance etc... can fix this.