Richard Dawkins, who coined the word in his book The Selfish Gene defines the meme as simply a unit of intellectual or cultural information that survives long enough to be recognized as such, and which can pass from mind to mind. There's not much of a sense of describing thought processes, but nor is it just a model. As Richard Dawkins writes (this is from memory), "God indeed exists, if only as a pattern in brain structures replicated across the minds of billions of people throughout the world." (Of course the patterns aren't physically identical, but they represent the same thing.)