In computer science, reflection is the process by which a computer program can observe and modify its own structure and behavior. The programming paradigm driven by reflection is called reflective programming.
At the lowest level, machine code can be treated reflectively because the distinction between instruction and data becomes just a matter of how the information is treated by the computer. Normally, 'instructions' are 'executed' and 'data' is 'processed', however, the program can also treat instructions as data and therefore make reflective modifications. Reflection is most common in high-level virtual machine programming languages like Smalltalk, and less common in lower-level programming languages like C.
Common types of reflection are runtime and dynamic, but some programming languages support compile time or static reflection.
Reference:
http://en.wikipedia.org/wiki/Reflection_%28computer_science%29
