An app stack refers to a set of software tools and applications working together to accomplish specific tasks or improve workflows. Commonly used in development environments, app stacks like LAMP (Linux, Apache, MySQL, PHP) or MEAN (MongoDB, Express, Angular, Node.js) help developers create, test, and run applications efficiently. The app stack provides seamless app switching, memory management, and enhanced functionality across devices. The Samsung App Stack is one example used for mobile app development and testing.