What is LaTeX2ε?
Lamport's last version of LaTeX (LaTeX 2.09, last updated in 1992) was superseded in 1994 by a new version (LaTeX2e) provided by the LaTeX team. LaTeX2e is now the only readily-available version of LaTeX, and draws together several threads of LaTeX development from the later days of LaTeX 2.09. The “e” of the name is (in the official logo) a single-stroke epsilon (, supposedly indicative of no more than a small change).
LaTeX2e has several enhancements over LaTeX 2.09, but they were all rather minor, with a view to continuity and stability rather than the “big push” that some had expected from the team. LaTeX2e continues to this day to offer a compatibility mode in which most files prepared for use with LaTeX 2.09 will run (albeit with somewhat reduced performance, and subject to voluminous complaints in the log file). Differences between LaTeX2e and LaTeX 2.09 are outlined in a series of “guide” files that are available in every LaTeX distribution (the same directory also contains “news” about each new release of LaTeX2e).
Development of the LaTeX2e kernel is somewhat limited by the need to retain compatibility with a very large ecosystem of third-party packages. However, recent developments (such as allowing Unicode input as-standard for documents) demonstrate that such change is still possible. Longer-term work is carried out by The LaTeX Project, with the aim of more substantial improvement to LaTeX.
Source: What is LaTeX2e?