Something that is monolithic is something created in one piece, resembling a monolith such as an obelisk. It mostly signifies artifacts without any subcomponents, i.e. a non-modularized, non-componentized, non-dismantable building block.
In computer programming, a monolithic program is a program built or shipped as one large program file or executable image. That is, it is not sectioned into a main program and supporting libraries. On modern systems, such a program might also be called statically linked.
In computeroperating systems, a monolithic kernel is a kernel which behaves as a single program, rather than as a collection of intercommunicating programs as in the microkernel design. The term "monolithic kernel" was coined as a mild term of abuse during a period in operating-systems research when microkernels were believed to be more advanced and capable.