Monolithic, in information technolog, means either very large (and possibly imposing) or composed all in one piece, depending on the particular context; the term is used in different ways to describe integrated circuits, organizations, applications and storage systems, among other things.
A few examples of how the term is used in IT:
A monolithic architecture is the traditional programming model, which means that elements of a software program are interwoven and interdependent. That model contrasts with more recent modular approaches such as a microservice architecture (MSA).
A monolithic storage array has disks fixed into the array frame and connected to controllers through cache memory; modular arrays, on the other hand, are usually based on dual controllers connected to a separate power source and connected to the disks through cables.
A monolithic corporation is a large, separate and undiversified organization.
In a general context, a monolith is a single, separate and large stone feature that may be geographic or man-made. Examples include a mountain that is not part of a range, a standing stone and a monument. The word comes from the Ancient Greek μονόλιθος (monolithos), from μόνος (one) and λίθος (stone).