1) In technical writing, information architecture is the set of ideas about how all information in a given context should be treated philosophically and, in a general way, how it should be organized. In the context of a company making computer products, an information architect might say that "All of our product information should serve customer needs as expressed by tasks that they have to do with our products," and would then develop a framework for organizing all existing and future product information in modules related to customer tasks. The results of this thinking would be expressed in an information architecture document.
For product information in the example just discussed, the information architecture document would become the foundation for information planning, which focuses on using the architecture for a specific division, set of products, or individual product. In addition to information architecture and information planning, information design focuses more narrowly on activities that support the architecture and planning, such as style guidelines, graphic design motifs, page design, and the information aspects of industrial design (labels, knobs, and other physical aspects of the user interface).
2) In Web site design, information architecture has a meaning similar to (1), but focused somewhat more narrowly on Web content as building blocks to be fit into a site's visual design and navigation scheme.
In technical writing in general and in Web site design in particular, information architecture is related to and generally supports the overlapping areas of content management, content distribution or syndication, and electronic publishing. Information architecture is also related to the treatment of information modules or building blocks as "objects" that can be described in one or a set of data definitions, typically using the Extensible Markup Language (XML). For example, an encyclopedic topic could be treated as a building block that could be distributed electronically using an XML definition that described each of the items in the topic (title, main content, author, date of authorship, and so forth).