Automatic configuration script produced by GNU Autoconf; automatically configures software source code packages to adapt to several types of Posix-like systems; created by testing a software package for each feature the program might need in order to run a specific system; Autoconf then builds a list of system features that the package requires.

Autoconf scripts are typically named "configure.ac." The automatic configuration script is created by running the preprocessor program m4 with the configure.ac file as input.