A technology stack is a combination of programming languages, frameworks, libraries, and tools used to develop and run applications. It typically consists of two main layers: the front-end, which is what users interact with, and the back-end, which handles data processing and storage. Common front-end technologies include HTML, CSS, and JavaScript, while back-end technologies might involve Node.js, Python, or Ruby on Rails. Choosing the right technology stack is crucial for a project's success, as it affects performance, scalability, and maintainability. Developers often consider factors like team expertise, project requirements, and community support when selecting a stack. Popular stacks include MEAN (MongoDB, Express.js, Angular, Node.js) and LAMP (Linux, Apache, MySQL, PHP).