From Joomla! Documentation
Like any computer or web application, Joomla! has its own terminology and ordinary English words may have particular meanings. For more terminology and meanings, see the Joomla! Glossary.
Section (deprecated after )
This the topmost “container” for content. Multiple categories can be placed into sections. The name can be appear within user friendly web addresses. So choose the names with care. You can create “blog” type formats that show articles in a tabular format.
Every category lives within a section(depreciated after ). Again the name can appear within user friendly web addresses. You can create blog type formats that use a tabular format. In Joomla! categories cannot "live" within other categories. From Joomla! Version categories can now contain subcategories making categories the topmost “container” for content.
These are where content lives. Every article is assigned to a category and section ( even if it is “uncategorised” ). Articles are only published when you decide it’s appropriate.
Most people start out creating articles in a standard desktop program - perhaps Microsoft Word. If you use this you should ensure you have filtered out the “Microsoft proprietary” HTML tags before pasting the content into the Article Editor. It can be easier to paste the content into Wordpad or Notepad, then save and then paste it onward - this has the same filtering affect. If you use the TinyMCE editor then the advanced option will show a "Paste From Word" button.
Look and Feel Terms
Templates determine the way the website appears - the colours, where things are on the page etc. Templates are normally constructed / bought when the website is created. It can be changed at will - so you may not need to change the content (in the articles) to change the appearance of the page. Most of this relies on Cascading Style Sheets and technical stuff - ask your advisor(s) if you’re interested.
Joomla templates are a series of rectangular boxes HTML elements called a <div>. These boxes can call pieces of content called Modules - each of which can have a unique name and/or template position. The exception is an article which normally is shown in the part of the screen not taken up by defined positions. e.g. the centre.
Be careful to use a good naming convention; as this can really help find the article appearing at a particular web address.
This is where the name of the page ( that appears in the web address ) is chosen, and where the layout is selected ( e.g., Blog, article, wrapper ). Some Search Engine Friendly URL systems may allow alternatives to this.
A page layout that allows web pages from external websites to be included without change. This can be good (because it’s quick) and bad (because the look and feel may be very different).