Computer programming is the process of writing, testing, debugging/troubleshooting, and maintaining the source code of comptuer programs.  This source code is written in a program language (ie C++, Java, PHP, etc.).  The code may be a modification of an existing source or something completely new.  The purpose of programming is to create a program that exhibits a certain desired behavior (customization).  The process of writing source code often requires expertise in many different subjects, including knowledge of the application domain, specialized algorithms and formal logic.