Microsoft SharePoint Portal Server Integration
Web Part Zones
The areas, or zones, are the locations on a SharePoint Web Parts page where Web Parts can be inserted. Web Part zones can contain one or more Web Parts.
Microsoft defines a Web Part zone as:
A container with a set of properties that can be configured to control the organization and format of Web Parts on a Web Part Page. Web Part zones can also be used to provide protection against changes to Web Parts.
Although their sizes are customizable, all Web Part pages contain these four Web zones.