This paper discusses the importance of definitions in the context of academic discussion, highlights the inconsistent terminology used to describe e-learning, and examines a range of different definitions of e-learning used by academic authors since 2011. Following an outline of the methodology, the paper identifies 15 unique definitions of e-learning in peer-reviewed papers published between January 2011 and December 2022. The 15 definitions are analysed for significant properties, and these properties are reviewed to assess whether they are essential components of e-learning. The paper then proposes a functional definition of e-learning, including all essential elements of e-learning and eliminating elements that may be present in some, but not all, instances of e-learning.