Bootstrap is the most popular CSS Framework for developing responsive and mobile-first websites.

SCSS is a preprocessor scripting language that extends the capabilities of CSS by adding features such as variables, nesting, and mixins. It allows developers to write more efficient and maintainable CSS code, and helps to streamline the development process by reducing repetition and increasing reusability.

A template or theme refers to a pre-designed layout or structure that provides a basic framework for building a specific type of application or website. It typically includes good design, placeholder content and functional features, allowing developers to customize and fill in the details according to their specific needs.

Pug is a high-performance template engine for Node.js and browsers that enables developers to write HTML templates using a concise and intuitive syntax. It supports a range of features, including template inheritance, conditionals, loops, mixins, and more, and can be easily integrated into a variety of web frameworks and build tools.