A heading is a word, phrase, or sentence at the beginning of a written passage that explains what it's about. A heading is very similar to a title.
A heading is similar to a caption, a line below a photograph that briefly explains it. Headings show up at the top of paragraphs, chapters, or pages, and they give you an idea of what the subject is. You might write a heading for each chapter of your novel, or on each page of your French club newsletter. The 1300's meaning of heading was "beheading," and it wasn't until the late 1800's that it came to mean "title."