In XML terminology, topic can mean 1. * A resource that acts as a proxy for some subject; the topic map system's representation of that subject. The relationship between a topic and its subject is defined to be one of reification. Reification of a subject allows topic characteristics to be assigned to the topic that reifies it. 2. * A short document which is written in such a way that it completely answers a single question. For example, an online help system typically consists of hundreds of topics, each describing a single procedure or concept. 3. * A element, used in many XML formats.