Behavioral patterns are patterns that describe how objects will communicate with each other. In other words, it is how one object will send information to another object, even if that information is just that some event has occurred. They help to lower the code's coupling by providing a more detached communication mechanism that allows one object to send information to another, while having as little knowledge about the other object as possible. The less any type knows about the rest of the types in the code base, the less it will depend on those types. These behavior patterns also help to increase cohesion by providing straightforward and understandable ways to send the information.
This can often be the difference between doing something, such as calling your sister to ask your mom to ask your grandpa what he wants for his birthday and being able to ask your grandpa directly because you have a good communication channel open with him. In general, we will want to have...