A subtopic is a topic that is part of a broader or more general topic. It is a division of a main topic and is used to break down a larger topic into smaller, more manageable parts. For example, a book may have ten main topics, each divided into four subtopics. Subtopics can be used to organize information and make it easier to understand. They can also be used to create a hierarchy of categories, such as in a forum or website. Subtopics are commonly used in academic writing, research papers, and presentations to help structure and organize information.