What's the difference between a Magento theme and a Magento skin?

What's the difference between a Magento theme and a Magento skin? What's the relationshiop between these and a Magento module?

Solution

A theme is any combination of layout, template, locale and/or skin file(s) that create the visual experience...

A theme consists of any or all of the following:

Layout (located in app/design/frontend/your_interface/your_theme/layout/) These are basic XML files that define block structure for different pages as well as control META information and page encoding.For in-depth look into layouts, read Intro to Layouts)
Templates (located in app/design/frontend/your_interface/your_theme/template/) These are PHTML files that contain (X)HTML markups and any necessary PHP tags to create logic for visual presentation.
Locale (located in app/design/frontend/your_interface/your_theme/locale/) These are simple text documents organized on a per language basis that contain translations for store copy.
Skins (located in skin/frontend/your_interface/your_theme/) These are block-specific Javascript and CSS and image files that compliment your (X)HTML.