R is a programming language specially designed for statistical computations, developed at the University of Auckland in New Zealand. It is entirely Free and Open Source community developed software.It is as powerful as commercial products like S-Plus, SPSS, Minitab or anything else in the statistical computing market. But because many programmers work on developing and improving R it is possibly a lot better and more powerful analytically than those commercial products. So I highly recommend that you pout some effort into learning R if you are at all interesting in ever using statistics software
The reason R is called "R" is because the other statistical computation software products begin with the letter "S", and "R" comes before "S" in the alphabet. Also, most of the R Language syntax is compatible with the commercial software S, which means R programmers can re-use their old code that was written in S without needing to make too many modifications. So it is a slightly cheeky name the creators of R thought up for their free software.