Someone once said that “a book without an index is like a country without a map”. However interesting and worthwhile the experience of driving from A to B without a map might be in its own right, there can be no doubt that when the goal is to arrive at one's destination as quickly as possible (or at least without undue delay), some kind of a map is indispensable. Similarly, if you are looking for a particular piece of information in a book (as opposed to enjoying the experience of reading it from cover to cover), a good index is an immense asset.
What it is a topic? A topic, in its most generic sense, can be any “thing” whatsoever – a person, an entity, a concept, really anything – regardless of whether it exists or has any other specific characteristics, about which anything whatsoever may be asserted by any means
Strictly speaking, the term “topic” refers to the element in the topic map document (the topic link) that represents the subject being referred to.
Topic Maps is an international industry standard (ISO 13250) for information management and interchange. Topic Maps is a Web 3.0 enabling technology. That means it works behind the scenes of many web portals and other rich data products.
The Topic Maps Data Model is the heart of the Topic Maps standards and is supported by several file formats, query languages and modeling languages.
A topic map in a software system is usually managed using a Topic Maps engine.