A Practical Definition of [Software] Design
Every application is a collection of code; the code’s arrangement is the design. Two isolated programmers, even when they share common ideas about design, can be relied upon to solve the same problem by arranging code in different ways. Design is not an assembly line where similarly trained workers construct identical widgets; it’s a studio where like-minded artists sculpt custom applications.
Design is thus an art, the art of arranging code.
- from Practical Object-Oriented Design - An Agile Primer Using Ruby, by Sandi Metz