Probably the question I get asked the most about R is, "What is R"? It's can be a hard question to answer, because R is so many things. It's data analysis software. It's an environment for data analysis. It's a language. It's an open-source project. It's a community. The Wikipedia page for R does a great job of describing the details of the features and history of R, but I was looking for something more concise that I could point people to when asked? I wrote up my take on the What is R? at inside-R.org.
Inside-R.org: What is R?