"There are many ways to give a function: by a formula, by a plot or graph, by an algorithm that computes it, or by a description of its properties. Sometimes, a function is described through its relationship to other functions (see, for example, inverse function). In applied disciplines, functions are frequently specified by their tables of values or by a formula. Not all types of description can be given for every possible function, and one must make a firm distinction between the function itself and multiple ways of presenting or visualizing it." This is a quote from: http://en.wikipedia.org/wiki/Function_(mathematics [Broken]) in the last sentence he mentions "one must make a firm distinction between the function itself and multiple ways of presenting or visualizing it." I`m now confused because when I think of a function I think of one of its representations e.g. formulas; the author says that I should make a distinction between the ways of presenting/visualizing and the function itself.. how do I do so? and when the word "function" is mentioned how should I interpret it in my mind?