A tech stack is significant in application development as it determines the tools and technologies used to build, operate, and maintain an application. It encompasses frontend, backend, and database technologies, each playing a vital role in performance and scalability. Choosing the right tech stack affects factors like development speed, maintenance costs, and team expertise. Furthermore, an optimal tech stack enables smooth integration with other tools and platforms, ensuring reliability and efficiency. The stack is a fundamental aspect of the development process and influences the final product's capabilities and user experience.