Onion Architecture
In plain terms
A layered design with the domain model at the center.
Going deeper
Onion Architecture places the domain model at the core, wrapping it in layers of services and infrastructure that depend inward. It's closely related to clean/hexagonal styles.
Under the hood
Dependencies flow toward the center; infrastructure is outermost and replaceable.
Examples
Domain-centric apps, dependency inversion, maintainable .NET/enterprise systems.
Think of it like...
Like an onion whose innermost layer (domain) is protected by surrounding layers.