Placeholders are a more flexible version of “contribution regions” from earlier releases. Placeholders were added in Site Studio 10gR4. A placeholder identifies where a region could be used for Contribution on a web page. Multiple placeholders may be added to a Page Template and identified by a placeholder name.
Each placeholder name has a placeholder definition.
A placeholder definition allows multiple Region Definitions and furthermore multiple Region Templates could be associated to each Region Definition
Region definitions are reusable groups of individual elements for a site content type.
Region templates are partial HTML files -i.e. no head and no body sections-, that define the layout and look-and-feel of the data in contribution regions within web pages.
This placeholder gets assigned a content file into it. This file is stored in the UCM Content Server and is called a Contribution Data File. Contributor data files are associated with a region definition to store the data for each element in the region definition.
A single placeholder on a web page can provide one of the multiple layouts associated to a placeholder (list of layouts determined by the Region Definitions associated to the placeholder definition).