Cyclomatic complexity

Cyclomatic Code Complexity was first introduced by Thomas McCabe in 1976. In 1976, Thomas McCabe published a paper arguing that code complexity is defined by its control flow. Since that time, others have identified different ways of measuring complexity (e.g. data complexity, module complexity, algorithmic complexity, call-to, call-by, etc.). Although these other methods are effective in the right context, it seems to be generally accepted that control flow is one of the most useful measurements of complexity, and high complexity scores have been shown to be a strong indicator of low reliability and frequent errors.

Some reference links:

Cyclomatic Code Complexity Analysis for Microsoft .NET Applications

http://www.codeproject.com/Articles/11719/Cyclomatic-Code-Complexity-Analysis-for-Microsoft