The answer is paper.
A sketch is a rough drawing or outline of something. A diagram is a drawing that shows the structure of something or how something works. A poster is a large printed advertisement or notice. A chart is a diagram that shows information in a way that is easy to understand.
Paper is a thin, flexible material that is made from wood pulp. It is used for writing, printing, and packaging.
The word “paper” is different from the rest of the words in the list because it is not a visual representation of something. The other words are all visual representations of something, either a rough drawing, a structure, an advertisement, or information.