A method in object-oriented programming is essentially a block of code that performs a specific task. It can take inputs, process them, and return a result. Methods are associated with objects and are used to expose behavior. In contrast, a class is a blueprint for objects, an attribute is a property or characteristic of an object, and a library is a collection of pre-written code that can be used to simplify development tasks. While classes and attributes are related to objects, and libraries may contain methods, the definition of a method itself is specifically a set of instructions that perform a task and can be called upon by an object.