When most people hear about behavioral patterns, it's often related to pet training or general behavioral psychology, which often boils down to biological entities doing what you want them to do. Well, in a way, all of coding is about programs doing what you want, so behavioral software design patterns cover a very wide range of behaviors that are, nonetheless, quite common in programming.

As an example, consider the domain of software engineering. We have languages that are compiled, which involves lexing, parsing, and a million other things (the Interpreter pattern), and having constructed an abstract syntax tree (AST) for a program, you might want to analyze the program for possible bugs (the Visitor pattern). All of these are behaviors that are common enough to be expressed as patterns, and this is why we are here today.

Unlike creational patterns (which are concerned exclusively with the creation of objects) or structural patterns (which are concerned with composition/aggregation/inheritance of objects), behavioral design patterns do not follow a central theme. While there are certain similarities between different patterns (e.g., Strategy and Template Method do the same thing in different ways), most patterns present unique approaches to solving a particular problem.