Monolith
also: monolithic architecture
An application built and deployed as a single unit — simple to start, harder to scale a large team on.
A monolith is an application built, deployed, and run as a single unit — all features in one codebase and one process. It is the simplest architecture and the right default for most new projects: one thing to build, test, deploy, and debug.
Worked example: a startup ships its whole app — auth, catalog, checkout — as one deployable service backed by one database; a developer runs the entire system locally and a single deploy ships everything. Gotcha: monoliths get painful only at scale — a large team stepping on each other in one codebase, one slow test suite gating all deploys, and no way to scale one hot feature independently — which is when microservices become worth their cost; splitting too early (before those pains are real) buys distributed-systems complexity you did not need. Prefer a well-modularized monolith first.