1) A cross section is a cut through something (such as a coaxial cable ) at an angle perpendicular to its axis in order to view its interior structure. A well-known example is a cross section of a tree that shows its growth rings and tells its age.
2) Somewhat less precisely, a cross section can be any view of something that shows a representative portion of each of its parts. For example, a cross section of a Web site might show a representative page of content at each of its hierarchical levels. A cross section of a Web site audience would indicate its demographics (types of people who used the site in terms of gender, age, occupation, and so forth).