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JavaScript is a high-level, interpreted programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS.

It enables interactive web pages and is an essential part of web applications. The vast majority of websites use it for client-side page behavior, and all major web browsers have a dedicated JavaScript engine to execute it.

Key Features:

• Dynamic typing
• First-class functions
• Prototype-based object-orientation
• Event-driven programming

CSS Flexbox (Flexible Box Layout) is a one-dimensional layout method for arranging items in rows or columns. Items flex (expand) to fill additional space or shrink to fit into smaller spaces.

Main Concepts:

• Flex Container: The parent element with display: flex
• Flex Items: The children of the flex container
• Main Axis: The primary axis along which flex items are laid out
• Cross Axis: The axis perpendicular to the main axis

Flexbox makes it easier to design flexible responsive layout structures without using float or positioning.

HTTP status codes are three-digit codes issued by a server in response to a client's request. They indicate whether a specific HTTP request has been successfully completed.

Common Status Codes:

• 200 OK: The request succeeded
• 201 Created: The request succeeded and a new resource was created
• 400 Bad Request: The server cannot process the request due to client error
• 401 Unauthorized: Authentication is required
• 404 Not Found: The server cannot find the requested resource
• 500 Internal Server Error: The server encountered an unexpected condition

Understanding these codes is crucial for debugging web applications and APIs.

Database normalization is the process of organizing data in a database to reduce redundancy and improve data integrity. It involves dividing large tables into smaller tables and defining relationships between them.

Normal Forms:

• 1NF (First Normal Form): Eliminate repeating groups and ensure atomic values
• 2NF (Second Normal Form): Meet 1NF and remove partial dependencies
• 3NF (Third Normal Form): Meet 2NF and remove transitive dependencies
• BCNF (Boyce-Codd Normal Form): A stricter version of 3NF

Proper normalization leads to more efficient database designs and easier maintenance.

REST (Representational State Transfer) is an architectural style for designing networked applications. It relies on a stateless, client-server protocol, almost always HTTP.

Core Principles:

• Stateless: Each request contains all information needed to complete it
• Client-Server: Separation of concerns between UI and data storage
• Cacheable: Responses must define themselves as cacheable or not
• Uniform Interface: Standardized way of communicating between components
• Layered System: Client cannot tell if connected directly to end server

RESTful APIs are widely used in modern web development for building scalable services.