These are the high-level blueprints. They define the fundamental structure of your entire system. (Example: MVC or Model-View-Controller, which keeps your data separate from your user interface).
Imagine you are designing a kitchen. You don’t need to reinvent the concept of a "triangle" between the sink, the fridge, and the stove. Architects have already figured out that this layout works best for cooking. That’s a pattern. Pattern-Oriented Software Architecture for Dummies
Are there any you're working on where you're struggling to organize your code? These are the high-level blueprints