Essential to XP, the small releases concept is all about offering new iterations of the product regularly. The goal is to have functional, yet minor updates ready to deploy every couple of weeks. This grants clients and teams the opportunity to gain feedback on the project's progress and direction. Having smaller updates minimizes the risk of issues and allows for course correction quicker than waiting for one large release.

Test-Driven Development (TDD) is a major XP practice where developers write tests before producing code. The developer first creates an initially failing automated test case that defines a desired functionality, then produces the smallest amount of code to pass that test, and finally refactors the new code to acceptable standards. TDD can reduce bugs and encourage simple and clearer designs. It ensures the software works throughout development.

Pair Programming is a technique of XP where two developers work together at a single workstation, often physically sitting side-by-side sharing a single computer. One developer, the 'driver', writes the code while the other, the 'observer' or 'navigator', reviews each line of code as they are typed in. The developers switch roles frequently. This practice encourages communication, reduces coding mistakes, promotes collective code ownership, and ensures high-quality code.

The practice of continuous integration is about frequently integrating code changes into a shared repository. Each change is then automatically built and tested to catch bugs as quickly as possible. Developers integrate their work frequently - usually each person integrates at least daily. With CI, teams avoid the pitfalls of 'integration hell' where attempting to bring together different parts of the project proves to be a time-consuming challenge.

On-Site Customer is the idea of having a representative of the end-user available to the development team at all times. This individual can answer questions, make decisions, and provide feedback rapidly, thereby minimizing the delay typically associated with these processes. This allows the team to make accurate and efficient decisions, reduce misunderstanding, and ensure that the product being developed is aligned with the end-users’ needs and expectations.

This XP concept puts importance on constant communication and collaboration among all members of the project, including the customer or their representative. Everyone is equally important for successful project development. Having the entire team work together ensures a mutual understanding of the project’s objectives and encourages faster and more effective decision making. The key to the functioning of the 'whole team' concept is regular and open communication, respecting everyone's opinions, and collective code ownership.

Coding Standards form a significant feature of XP. This concept ensures that all developers write code in the same way, promoting readability and understanding across the team. This technique is crucial for XP practices like pair programming and refactoring. The key goal is to reduce complexity in the code and allow any developer to easily understand and work on any part of the project. This concept makes it easier for everyone to maintain and modify the code when necessary.

Collective Ownership infers that the codebase is owned collectively by all developers working on the project. Any developer can make changes to any part of the codebase at any time. This practice promotes shared responsibility for the product among all team members. It can increase productivity and helps avoid development bottlenecks. Changes made by any developer can be corrected, improved, or validated by others, which also promotes knowledge sharing and learning within the team.

The practice of making 'Continuous Small Improvements' is another interesting facet of Extreme Programming. It encourages teams to never leave things to be 'fixed later' and instead, make small, incremental changes on a regular basis to continuously improve the code base. This constant evolution helps to keep technical debt in check, thereby ensuring the general health and quality of the project.

Metaphor in XP refers to using simple, shared stories of how the system works to guide its creation and the communication among team members. Using a commonly understandable metaphor helps avoid misunderstandings and ensures everyone has the same broad understanding of how the system should behave. This shared vision helps facilitate communication and collaboration in the team.

System Metaphor is a concept which involves providing a simple explanation of how the system works. It is intended to help developers understand the system’s architecture by relating it to an experience or concept they already understand. The metaphor guides the system design and helps newcomers to understand and navigate the code base. This also facilitates communication and shared understanding among team members.

Feedback in XP is about continually validating decisions by receiving rapid feedback. This feedback loop is critical and can be through different methods such as pair programming, testing (both automated unit tests and functional tests), integration and feedback from customers or other stakeholders. The concept of feedback ensures that the development is in line with the customer's needs and any errors or misconceptions can be quickly identified and corrected. It saves time and resources as errors are identified early in the development process.