To understand what a bookmark is, one needs to know about internet browsing. A bookmark, as commonly used in web browsers, is a feature that allows the user to save the address of a particular web page to make it easier to revisit later. Now, let's go through each option and explain why it is right or wrong:

A. Window where workspace shortcuts are stored: This option is incorrect. A window where workspace shortcuts are stored is commonly referred to as a workspace or a dashboard. It serves as a central location for accessing frequently used files and applications.

B. A bookmark is a thin marker to add icons: This option is incorrect. A thin marker to add icons is not a bookmark. It does not allow the user to save the address of a particular web page for later reference.

C. Bookmark is an icon: This option is incorrect. A bookmark is not an icon, but rather a saved URL that allows quick access to a web page.

D. A customizable, graphical link to databases, views, documents, applications, and web pages: This option is correct. A bookmark is a customizable, graphical link that allows users to easily access databases, views, documents, applications, and web pages. It is a convenient way to save and organize frequently visited websites and pages.

The Answer is: D