meaning of include file

Hi I am trying to install the PETSc package on my Ubuntu 10.04 laptop. I am trying to configure it with the external solver SuperLU.

One of the instructions for the options to include while doing configure/make in the PETSc webpage is the following:

--with-PACKAGENAME-include=INCLUDEPATH --with-PACKAGENAME-lib=LIBRARYLIST: Usually a package is defined completely by its include file location - and library list. [If the package is already installed] - then one can use these two options to specify the package to configure.

I do not understand what the include file means. Is this some sort of header file? How does it look like?

I am new to installing and using numerical software so a detailed answer will be helpful.

I think this fits better on superuser (and I'm voting for migration), but yes, include files (in C) are header files.

You can recognize them by the .h (or rarely .hpp for C++ header files) extension. You usually find them in /usr/include or /usr/local/include, depending on your system.