In everyday language, you can use the word model in various ways---fashion model, model airplane, model student—but scientists use the word in a very specific way. A scientific model is a carefully devised mental conception of how something works, a framework that helps scientists think about some aspect of nature. For example, astronomers use the celestial sphere as a way to think about the motions of the sky, sun, moon, and stars.
Although a scientific model is a mental conception, it can take many forms. Some models are imprecise—the psychologist’s model of how the human mind processes visual information into images, or instance. But or other models are so specific that they can be expressed as a set of mathematical equations. or example, an astronomer might use a set of equations to describe in detail how gas falls into a black hole. You could refer to such a calculation as a model. Of course, you could use mental and plastic to build a celestial globe, but the thing you build wouldn’t really be the model any more than the equation are a model. A scientific model is a mental conception, an idea that helps you think about nature.