# OOP glossary: Master level

12 OOP terms at the Master level, each with a short definition and a link to its full page.

Updated: September 27, 2026

[Study these as flash cards](https://www.ask-codey.com/decks/oop/master)

- [Aggregate Root](https://www.ask-codey.com/glossary/aggregate-root): The single entry object for a group of related objects, guarding their rules.
- [Anemic Domain Model](https://www.ask-codey.com/glossary/anemic-domain-model): Classes that hold only data while all the business rules live somewhere else.
- [Command Pattern](https://www.ask-codey.com/glossary/command-pattern): A pattern that turns an action into an object so it can be queued or undone.
- [Covariance and Contravariance](https://www.ask-codey.com/glossary/covariance-and-contravariance): Rules for when a more specific or more general type can stand in for another.
- [Diamond Problem](https://www.ask-codey.com/glossary/diamond-problem): The confusion when a class inherits the same method through two parents.
- [Domain-Driven Design](https://www.ask-codey.com/glossary/domain-driven-design): Designing code around the real business, its vocabulary and its rules.
- [Entity](https://www.ask-codey.com/glossary/entity-oop): An object defined by a lasting identity (an ID), not by its values.
- [Fragile Base Class Problem](https://www.ask-codey.com/glossary/fragile-base-class-problem): When a change to a parent class unexpectedly breaks its child classes.
- [Inversion of Control Container](https://www.ask-codey.com/glossary/inversion-of-control-container): A framework tool that creates objects and supplies their dependencies automatically.
- [Object Pool](https://www.ask-codey.com/glossary/object-pool): A set of ready-made objects that are reused instead of created fresh each time.
- [Template Method Pattern](https://www.ask-codey.com/glossary/template-method-pattern): A pattern where a base class fixes the steps and child classes fill some of them in.
- [Visitor Pattern](https://www.ask-codey.com/glossary/visitor-pattern): A pattern that adds new operations to classes by moving them into visitor classes.

- Previous level: [Freelancer](https://www.ask-codey.com/glossary/subjects/oop/freelancer)

[Every OOP term, by level](https://www.ask-codey.com/glossary/subjects/oop)

Source: https://www.ask-codey.com/glossary/subjects/oop/master