define helps you create 'define.pdf' and associated file tree for FDA-style submission of analysis datasets, etc. It converts csv files to SAS Transport V. 5 'xpt' format, using metadata encoded in a specification file. It enforces the 'txt' extension for other (presumably ASCII) files.
The only function you're likely to need from define is
define. You may want to learn more about
metadata encoding from encode and more about
specification files from spec.