'Back-End Development' pertains to the server-side development of web applications, focusing on databases, scripting, and website architecture. This is where the core application logic, data storage, and processing take place. It’s the unseen part of the application, powering the visible front-end or client-side experience.

Back-end development involves creating and maintaining the technologies that power the components enabling the user-facing side of the website to function. This includes database interactions, computations, and performance optimization. Back-end developers utilize server-side languages like PHP, Ruby, Python, Java, and .Net, and manage data with tools like MySQL, Oracle, and SQL Server.

A crucial aspect of back-end development is building APIs for front-end to server-side communication. Back-end developers are also tasked with creating secure and robust data storage solutions to ensure data integrity and security.

Back-end development is key to web application functionality, handling user requests, executing application logic, managing database operations, and ensuring overall application performance and security.

To sum up, back-end development is the backbone of web applications, handling the crucial 'behind-the-scenes' functions that enable the user-facing components to exist and perform effectively. It encompasses a broad range of skills and technologies crucial to comprehensive web development.