Learning is mostly asynchronous 

Mostly online learning is asynchronous. For example online courses are prepared beforehand by educators, with students accessing them as and when they like and choose. Material presented on a web page can be read at any time.

The fact that students can learn at any time, not necessarily when the educator is available, is one of the main advantages of online learning. This provides great flexibility and increases availability of learning.

Most definitions emphasize that online learning is delivered through Internet or web-based mediums (Moore et al., 2010; Ryan and Young, 2015; Lee, 2017).

Distance learning

Online learning is also for the most part also distance learning. The students are physically separated from the educator as they are learning. Students might be present in a different building, a different part of a town, or even much further afield and in a different country!

Unlimited student numbers

There is practically no limit in terms of numbers for some forms of online learning! Once they have been developed online learning courses can be accessed by large numbers of people. A 'live' webinar can be watched by thousands of people at once. A prerecorded video can be viewed by many thousands.

Freedom of time

Because of the asynchronous nature of most online learning, most courses can be started or continued whenever you want. This offers unlimited freedom to learners. There is no constraint having to wait for the next semester in order to start. Students can start learning whenever it is suitable for them.

This flexibility also fits perfectly into modern life. We all have constraints on our time, and typically these increase as we get older. The nature of online learning means we can fit education around work and family commitments.

Student centered

Online learning promotes more student centered learning. In the scenario of a traditional classroom it is almost inevitably the educator who (following a syllabus) decides how to teach. They decide what order to do things and how to go about day to day teaching. It some situations they even choose what is actually to be taught!