What is the difference between a Layout, Sublayout, and Rendering?

Question

In Sitecore, under /sitecore/layouts, I see the following:

• Layouts
• Sublayouts
• Renderings

What are these, and what makes them different? Are there any other types of layouts?

Answer 1

Layouts

• Provide the outermost HTML structure of a page.
• There is one layout (per device) per page.
• Apply to WebForms (.aspx) and MVC (.cshtml)
• Comprise of Layout definition item and aspx page (WebForms) or cshtml file (MVC)

Sublayouts

• Provide inner HTML structure to a component or structuring element of a page.
• Apply only to WebForms
• Comprise of a definition item + .ascx control.
• Can contain nested Sublayouts within their placeholders

Renderings

• Provide inner HTML structure to a component or structuring element of a page.
• Can be used with WebForms (if using XSLT) OR MVC
• Sitecore MVC uses the following rendering sub-types:
  • Controller rendering: rendering definition item references a controller and action name
  • View rendering: rendering definition item references a view (cshtml file) and optionally a viewmodel (which in turn references a model type in code)
  • Item rendering: rendering definition item does not reference a controller or a view, instead it serves as a kind of 'placeholder'. The datasource item should have a rendering type associated with it via the __renderers field. Setting the datasource of an item rendering causes Sitecore to look at the datasource item itself to decide which rendering to use.
• Comprise of a definition item + .xslt or .cshtml view
• Can contain nested renderings (or sublayouts [1]) within their placeholders

[1] can only contain nested sublayout if xslt rendering within a WebForms solution

More information on MVC-specific aspects can be found here: http://www.matthewdresser.com/sitecore/sitecore-mvc-presentation-concepts