A tool for finding information or "pages" on the World Wide Web. Usually consists of a hierarchical list of topics.

a web site which provides links to information on the Internet organized by topic

A Subject Index or Subject Catalog is a service that organizes linked documents by their content and subject matter. Organized into general categories (or alphabetically) at the top level, documents are layered hierarchically and collected with related pages. Although any subject index may be smaller than a searchable one, it is generally a much more reliable tool.

a selection of web pages, usually arranged by subject or within a specific subject area