The Singleton design pattern ensures that a class has only one instance and provides a global point of access to it. This is useful when exactly one object is needed to coordinate actions across the system.

Two-factor authentication adds an extra layer of security to the authentication process. It typically involves something the user knows (password) and something the user has (a code sent to their mobile device), enhancing security.

The transform property in CSS is commonly used to improve rendering performance by minimizing layout recalculations. It enables developers to apply 2D and 3D transformations to elements without triggering costly repaints or reflows. This can significantly enhance the performance of web pages, especially during animations.

Browser Developer Tools provide a hierarchical view of the Document Object Model (DOM). This view helps developers understand the structure and relationships of HTML elements on a webpage.

In Object-Oriented Programming (OOP), a class is a blueprint for creating objects. Objects are instances of a class and encapsulate both data (attributes) and behavior (methods) related to that class.

The alt attribute is used to provide alternative text for an image in HTML. This text is displayed if the image fails to load or for accessibility purposes, allowing screen readers to describe the image to visually impaired users.

A design pattern in software engineering is a general reusable solution to a commonly occurring problem within a given context in software design. It represents best practices and provides a template for solving particular issues.

The "git rebase -i" command allows for Rewriting commits interactively. It opens an interactive interface where you can squash, pick, edit, and reorder commits, providing flexibility in managing commit history.

React makes use of a virtual DOM to efficiently update the actual DOM. The virtual DOM is a lightweight copy of the real DOM, and changes are first made to the virtual DOM for faster updates.

Best practices for testing responsiveness involve using browser developer tools, utilizing online testing tools, conducting real device testing, and simulating different viewports to ensure compatibility across a variety of devices and screen sizes.