User stories represent a high-level definition of requirements in a BDD approach. This concept involves defining features from the perspective of end-users. User stories are written in a simple and non-technical language that focuses on the value a user gets from a feature rather than how that feature will be implemented. A typical user story includes a type of user, the desired feature or action, and the expected benefit or value.

Living Documentation in BDD refers to the concept where system documentation is automatically updated as software evolves. It is rooted in practical examples and expected behavior of the system from user perspectives. The living documentation serves as the source of truth for anyone involved in the project, which ensures that all team members understand the software behavior.

Ubiquitous language represents a common body of terminology used by all stakeholders in the project. The concept encourages project members to use the same language to describe the system, reducing ambiguity and misunderstanding. By focusing on common language, BDD ensures that the project team and stakeholders have a unified understanding of the requirements and functions of the software.

The term 'Three Amigos' refers to a collaborative meeting format in BDD practices that often involves three roles: the product owner or business analyst, a developer, and a tester. The purpose of these meetings is to define and refine user stories, discuss potential edge cases, and agree upon the desired behavior of a feature. This collaboration ensures that all perspectives are considered before the implementation phase.

BDD leans heavily on automated testing as a method of verifying the expected behavior of a system. Automated tests are written based on user stories and form an essential part of the living documentation. These tests are run automatically whenever changes are introduced to the codebase, providing quick feedback on whether the code meets requirements and alerts regarding potential functional issues before code is deployed.

Scenario Mapping, a crucial concept in Behavior Driven Development (BDD), is the process of defining and visualizing potential user scenarios associated with a particular function or feature of a project or application. It involves eliciting requirements through the exploration of real-world use cases, and translating these into clearly defined scenarios that can guide development and testing. It fosters shared understanding of the requirements between stakeholders, project team members and developers. Scenario Mapping also facilitates test-driven development, enabling developers to create scenario-specific tests that can verify the correct functionality of the developed feature.

SpecBDD, an extension of BDD, focuses on defining the specifications of the software being developed. The nomenclature in SpecBDD comprises of 'specifications' instead of 'tests', focusing on the 'behavior' aspect of BDD. It essentially promotes communicating software expectations with examples. This often involves writing human-readable stories that describe the behavior of your application, followed by an automatic process of turning those stories into executable tests. These executable tests are written before the code, supporting a test-first approach, and can also serve as living documentation are created.

Acceptance Test-Driven Development (ATDD) is fundamental to the BDD approach. It involves discussion among the stakeholders (including customers, developers, testers, analysts) to collaboratively define acceptance tests based on user requirements. The acceptance tests define the functional behavior of the system and are written in advance of the system being implemented. These tests are used as the primary means of communication, removing ambiguities and resolving confusions about the intended behavior of the software. ATDD encourages team collaboration and helps to ensure that all functions have been fully understood before development begins.

In behavior-driven development, outside-in development emphasizes the value of obtaining stakeholder feedback and ensures the software is built with the user's concerns at the forefront. This approach begins by defining a vision of the software based on stakeholder feedback, then gradually explores the software behavior in detail. The first step in the outside-in development method includes defining the system's user interface and the interaction with external systems. Next, the behavior of the software's components that directly support the interfaces is defined. Lastly, those aspects that do not directly support the interfaces are developed. This process is particularly suitable for managing complex systems where high-level information flow is established first, followed by detailed behavior.

Gherkin, often used in BDD, is a simple, domain-specific language for describing business behavior without getting into details of implementation. It provides a uniform pattern for specifying behavior, and its syntax is easily readable and understandable by business stakeholders, analysts, testers and developers. This encourages active stakeholder participation, promotes effective communication and reduces misunderstandings. Each behavior is described by a scenario, structured around a context, an event and an outcome, written in a Given, When, Then and And format. This can then be directly converted into an automated test script. As a result, the gherkin language helps in maintaining active stakeholder engagement and streamlines the delivery of the expected business values.