Root Cause Analysis is a problem solving activity where an explicit attempt is made to identify the root cause of a particular fault or issue.
In software development, unless a bug has always existed in a particular piece of functionality, there will always be a single attributable root cause. Identifying this route cause is not always easy and unless you have spent enough time analyzing a particular bug it is hard to know if the fix you are about to propose for the bug is fixing the root cause of the bug or just one of many potential symptoms.