Moodle is a Virtual Learning Environment (VLE). It is essentially a website that facilitates the delivery of content and activities to students, through the provision of a range of built in tools and functions.
Moodle can be used to deliver anything from a wholly online course (pure elearning) through to one that supports aspects of traditional, face-to-face interaction (blended learning).
Whilst Moodle is commonly used to provide students with access to content, it can also facilitate the creation of collaborative learning communities around specific subject areas. One of its greatest strengths is the ease with which it can support a more active approach to learning through the use of forums, wikis, quizzes etc.