Private methods are functions defined within a class that are not accessible from outside that class. They are used to encapsulate functionality that should not be exposed to the outside world, helping to maintain the integrity of the class's internal state. By keeping certain methods private, developers can prevent unintended interference and ensure that the class operates as intended. In programming languages like Python and Java, private methods are typically indicated by specific naming conventions or access modifiers. This practice promotes better organization and modularity in code, making it easier to manage and understand complex systems while reducing the risk of errors.