In programming, it’s often useful to divide a task into parts, and consider the overall program as a combination of small tasks. Each small task can be considered a subset of the overall program, to be called upon when needed. In programming lingo, that’s often called a “subroutine” or a “function”.

In Max, you can encapsulate a patch consisting of several objects inside a single Max patcher object. The contents of that patcher object can be thought of as a “subroutine” of the main patcher. Inside the patcher object, you can create inlet and outlet objects, which will appear as inlets and outlets of the patcher object in the main patch.

p is a synonym for patcher

You can view and edit the contents of a patcher object by double-clicking on it in the locked patcher window.

A patcher object could potentially even include other nested patcher objects. Dividing your overall task into separate tasks (subroutines) and encapsulating each one as an object is a good way to organize your program.