Moodle is a free, open source learning management system that enables you to create powerful, flexible, and engaging online learning experiences. I use the phrase online learning experiences instead of online courses deliberately. The phrase online course often connotes a sequential series of web pages, some images, maybe a few animations, and a quiz put online. There might be some email or bulletin board communication among the teacher and students. However, online learning can be much more engaging than that.
Moodle's name gives you an insight into its approach to e-learning. The official Moodle documentation on http://docs.moodle.org states the following: