GLib is a cross-platform software utility library (development files)
GLib is a cross-platform software utility library that began as part of the GTK+ project. However, before releasing version 2 of GTK+, the project's developers decided to separate non-GUI-specific code from the GTK+ platform, thus creating GLib as a separate product. GLib was released as a separate library so other developers, those who did not make use of the GUI-related portions of GTK+, could make use of the non-GUI portions of the library without the overhead of depending on the entire GUI library.
Since GLib is a cross-platform library, applications using it to interface with the operating system are usually portable across different operating systems without major changes.