"Pattern in architecture is the idea of capturing architectural design ideas as archetypal and reusable descriptions. The term "pattern" is usually attributed to Christopher Alexander, an Austrian born American architect. The patterns serve as an aid to design cities and buildings. The concept of having collections of "patterns", or typical samples as such, is much older. One can think of these collections as forming a pattern language, whereas the elements of this language may be combined, governed by certain rules."
Above is another definition for "pattern". Christopher Alexander's pattern language seems to have been quite influential in various disciplines, for example in computer science. I do not know enough about it yet, but at first reading it reminds me of the aspect of "pattern" as a "blueprint", which "pattern" for example has on http://www.ravelry.com/. In knitting I personally would always rather call this "instruction": How to knit this hat, jumper etc.
The meaning of "pattern" is somewhat oscillating it seems. For me the most interesting aspect is the inherent quality and characteristics of a pattern. But, like patterns in nature can be found on and in many individuals, a pattern created by humans can be used for many situations or entities, that's were the "blueprint-pattern" meaning derives from. And in between are the "patterns" that can be "observed" on many levels: behaviour, weather, society, history, economy etc. Some of these aspects seem also to be part of Alexander's pattern language.
In today's house I used a different "pattern", I could say: a steeper gable. The "pattern" (the instruction) for this would tell you to decrease only in every fourth row for the gable. The "pattern" (the instruction) for the "stitch pattern" is given below.