The category of people a periodical or book is targeting as potential readers. Every periodical has a specific target audience, such as preschoolers, parents, senior adults, teenagers, etc. As a writer, it is critical that you understand what the target audience is for any publication you write for, as well as knowing enough about that audience to write to their needs or interests. To ignore the target audience means you are unlikely to sell to that periodical.
When writing a book, a common mistake is doing so without a specific target audience in mind. Before starting a book, be sure you have that target audience clearly in mind and gear the content of the book to their interests. One of the questions a publisher will ask upfront is who you see as your target audience. You want to be able to identify a very specific target. Never say “All Christians,” or “All women,” or “All children.” Such statements will result in a swift rejection. A publisher wants to know what specific group of people they can market the book (and their advertising) to—who is going to buy your book? For example: parents of teenagers, pastors, children 8-12 years, college students, etc. For help in defining your target audience, go to: http://www.writersdigest.com/qp7-migration-all-articles/qp7-migration-fiction/learn_to_write_for_a_target_audience.