If interactivity is the defining characteristic of the Internet in general, linking is the defining characteristic of the Web in particular. By creating hypertext documents and including links to related information within or outside their sites, Web authors can greatly multiply the information they provide.

Anybody who uses the Web quickly becomes aware of these links. But you may not be aware of the different types of links or how some can even create legal liability for Web authors, whether they’ve created a business or a personal site.

The most common type of external Web link takes you to the opening page or home page of another Web site. The authors of those sites are usually greatly appreciative of other sites that link to their sites in this way. This type of linking is used by Google and other Web search engines to determine which Web sites they list first. Being included among the first page of sites returned in a Google search can be crucial for a site’s success.

But some links aren’t as appreciated. Some Web sites link not to the home page of another site but to an image or to text within that site, and they make it seem as if this content is an integral part of the linking site. These are typically referred to as direct links or inline links, and the practice of using them is sometimes referred to as bandwidth theft.

Bandwidth is being stolen because the Web site doing this type of linking does it typically without permission and often without crediting the linked site. It’s also considered stolen because it increases the use of the linked site and possibly its maintenance costs without providing it any benefits.

It can also be a copyright violation, resulting in a nasty “cease and desist” letter, and it has been known to prompt Internet service providers and Web hosts to shut down a site that has been caught doing this.

There are technical means to prevent content of yours from being inline linked in this way. A code determines when a link request is coming from another site and automatically supplies different content, such as the message “Don’t direct link.” In other cases, when a Web author has discovered that another site has engaged in image theft, he or she may manually replace the image that’s being linked to with a “shock image” to try to teach the other site a lesson.

Another type of link that isn’t as clear-cut is called a deep link. Here, a Web site doesn’t link to the home page of another site but to one of its internal pages. This practice has generally been considered acceptable since the Web went public in 1991. It benefits surfers because it takes them directly to the relevant content a Web author is linking to.

But some commercial Web sites have objected to this practice and have even sued other sites that have done this (most notably Ticketmaster). Other site owners have objected to deep linking because they want surfers to enter their site through its ad-revenue-generating home page and other internal pages.

As a result, some legal experts recommend that Web authors who want to create a deep link to another site ask permission first, according to Jeanne Jennings (http://www.jeannejennings.com), an online marketing consultant in Washington, D.C., who advises medium to large companies with an Internet presence. In a phone interview, Jennings said a less cumbersome approach is to check that the site doesn’t have a posted policy against deep linking. That’s what she recommends to her clients.

Links on a Web page may appear and work differently depending on which browser you’re using, how you have it configured, and how the Web author of the page has coded the link.

Words that are linked to other pages or sites usually appear in a different color, style (underlined, bold, etc.), or font. The color of the linked word usually changes after you’ve clicked on it, indicating that you’ve already been to the target page or seen the target content. This happens because the link is being temporarily stored in a part of your computer’s memory called a cache.

When you click on a link, normally the new page replaces your current page. But Web authors frequently code some of their links so that clicking on one opens up a new browser window on your screen. Web authors do this in particular when linking to external sites.