The significance of a tech stack in software development lies in its foundational role in determining how applications are built and function. A tech stack consists of a collection of programming languages, frameworks, libraries, and tools used to create a software application. It affects development speed, scalability, performance, and maintainability. A well-chosen tech stack aligns with project requirements and team skillsets, enabling efficient collaboration and fostering innovation. Additionally, the tech stack influences the application's architecture and can impact overall user experience and responsiveness, making its selection crucial for success.