Synchronous Learning occurs at a specific time when learner and teachers engage in live instruction and learning activities. Examples include web conferences, chat, instant messaging. When a learner can choose when to engage with the learning materials and activities, this is called asynchronous. Examples of this include, watching videos, projects, email, discussion boards, self paced units (e.g. Khan Academy). Both synchronous and asynchronous learning can and should be used in e-learning.
William Horton offers a framework for e-learning comprised of Absorb, Do, Connect. His website offers examples of each component. The University of Massachusetts, Boston recommends using absorb activities for asynchronous learning and a combination of synchronous and asynchronous opportunities for the do and connect components of the framework.
A study of asynchronous and synchronous e-learning methods discovered that each supports different purposes
By Stefan Hrastinski