The glibc package contains standard libraries which are used by multiple
programs on the system. In order to save disk space and memory, as well as to
make upgrading easier, common system code is kept in one place and shared
between programs. This particular package contains the most important sets of
shared libraries: the standard C library and the standard math library.
Without these two libraries, a Linux system will not function.
Kernel-headers includes the C header files that specify the interface between
the Linux kernel and userspace libraries and programs. The header files
define structures and constants that are needed for building most standard
programs and are also needed for rebuilding the glibc package.