From Joomla! Documentation
The "J1.5" namespace is an archived namespace. This page contains information for a Joomla! version which is no longer supported. It exists only as a historical reference, it will not be improved and its content may be incomplete and/or contain broken links.
In Joomla! versions up to and including , a Section is a collection of Categories. It is the top level in the hierarchy Sections -> Categories -> Articles. For example, a website might have Sections called "Animals" and "Plants". Within the "Animals" Section, the website might have Categories such as "Birds" and "Mammals".