A paragraph style that is displayed in a large, bold typeface. Having text containing keywords in the Heading Tags can improve the search engine ranking of a page for those keywords. Text that is visible to the search engines but is invisible to humans. Mainly accomplished by using text in the same color as the background color of the page. Primarily used for the purpose of including extra keywords in the page without distorting the aesthetics of the page.
Most search engines penalize web sites which use such hidden text.
An image containing one or more invisible regions which are linked to other pages. If the image map is defined as a separate file, the search engines may not be able to index the pages to which that image map links. The way out is to have text hyperlinks to those pages in addition to the links from the image map. However, image maps defined within the same web page will generally not prevent search engines from indexing the other pages. A database of sites used by many of the larger search engines like Hotbot, MSN etc.