Refactoring Perl code
Gabor Szabo will give a talk at YAPC::Europe 2012 described as
Code refactoring is "disciplined technique for restructuring an existing body of code, altering its internal structure without changing its external behavior". It is needed to ensure your code remains readable while growing in size and scope.
It is needed if you have some old code base that needs improvement and after every period of intense development when you "did not have the time to properly design your code".
There are several patterns in refactoring, some of them you might already practice without knowing the name.
The most obvious is when you use a variable $x and suddenly you realize it could have a more descriptive name.
If you change all the occurances of $x to this better name, without changing anything else in the code, that's already refactoring.