Informational/explanatory writing conveys information accurately. This kind of writing serves one or more closely related purposes: to increase reader's knowledge of a subject, to help readers better understand a procedure or process, or to provide readers with an enhanced comprehension of a concept.
Informational/explanatory writing addresses matters such as types (What are the different types of poetry?) and components (What are the parts of a motor?); size, function, or behavior (How big is the United States? What is an X-ray used for? How do penguins find food?); how things work (How does the legislative branch of government function?); and why things happen (Why do some authors blend genres?). To produce this kind of writing, students draw from what they already know and from primary and secondary sources. With practice, students become better able to develop a controlling idea and a coherent focus on a topic and more skilled at selecting and incorporating relevant examples, facts, and details into their writing. They are also able to use a variety of techniques to convey information, such as naming, defining, describing, or differentiating different types or parts; comparing or contrasting ideas or concepts; and citing an anecdote or a scenario to illustrate a point. Informational/explanatory writing includes a wide array of genres, including academic genres such as literary analyses, scientific and historical reports, summaries, and precise writing as well as forms of workplace and functional writing such as instructions, manuals, memos, reports, applications, and resumes. As students advance through the grades, they expand their repertoire of informational/explanatory genres and use them effectively in a variety of disciplines and domains.
Source: CCSS for ELA Appendix A