This is a monolith:
It is big, of one piece, and grows vertically. It would probably be difficult to reshape, or otherwise modify without great effort, great danger, and great cost. When someone describes an architecture as monolithic, they are using the preceding metaphor to suggest something very large and immovable and so massive as to discourage those attempting to improve it or to survey its total constituent parts in a comprehensive way.
Consider a simple application, like a to-do list. A list manager requires functionality to create, add, delete, and otherwise change lists. The code for that application might resemble this ...
