When we say “R Markdown”, we usually refer to the rmarkdown package, which is based on Pandoc and knitr. Prior to the rmarkdown package, there actually existed an older version of R Markdown, which was based on the markdown package instead of Pandoc. Later we called this version “R Markdown v1”.
R Markdown v1 was more or less an experiment, although many people liked it (perhaps because they had suffered for too long from LaTeX). It did not take long before we started developing v2, i.e., …