A programming language developed by the statistics group at Bell Labs for interactive data analysis. The S language pioneered interactive statistical analysis and visualization. A commercial version, S-PLUS, is sold by Mathsoft.
The S language is extremely useful in exploratory data analysis due its data manipulation capabilities and huge library of statistical and graphical routines. Unlike statistical packages such as SPSS, S is an object-oriented programming language. Unlike SAS, S is interactive and doesn't work with with large data sets, so it's naturally more appropriate for exploratory analyses. S is most similar to systems such as Matlab and Mathematica.