On Unix and related systems, a file that is run before make and make install. Often, but not always, this file is a sh shell script generated by autoconf.
If you obtain code from a CVS repository (or a file built from the CVS repository), you may find that while the instructions talk about running a command called configure, there isn't such a file. If, however, there is a configure.in file, that means that the configure.in and autoconf, together, may generate the configure. I say may because there often are several programs that one ends up needing to have to be able to build configure. For instance, one frequently needs the m4 command (a macro preprocessor). [fill in the names of the rest of the suite of programs needed as a part of configure]
When building older Tcl versions or Tcl extensions based on TEA, ./configure might fail with an error resembling:
./configure: line 7624: syntax error near unexpected token `)'
See bash for explanation and the simple solution.