What is R: R language is widely used among statisticians and data miners for developing data analysis software.
What is R Markdown : R Markdown is a tool designed to help create reproducible, dynamic reports with R. An R Markdown document is written in markdown (an easy-to-write plain text format) and contains chunks of embedded R code.
Why using R and R Markdown : As data scientists, we often have repeated analysis to perform (example: validation of analytical methods). Automating such routines could be a good way to reduce the likelihood of human errors that often arise while performing numerous repetitive tasks and divert resources from boring copy/paste type of exercises to challenging problem solving.