There are a number of established companies producing what are, for the purpose of this book, called Virtual Learning Environments. There are also a few emerging commercial brands and some open source alternatives that are gathering recognition in the education sector. WebCT and Blackboard are probably the most well known of the commercial products, and Moodle is the best known free, open source alternative.
In most cases, you will find that the term Virtual Learning Environments can be used interchangeably with other terms such as Managed Learning Environments (MLE), Course Management Systems (CMS), Learning Support System (LSS), Learning Platform (LP), and Learning Management Systems (LMS). Although I prefer to keep it like that to makes things easier, there are subtle differences between these systems.
The one that really is different is an MLE, which is a system that is used to manage all of the ICT systems of an institution relating to the students' education, such as the student records MIS system and the VLE. So in these terms, a VLE or CMS would be a part of an MLE, being that the MLE manages all of the related student records and educations systems.