The role of a tech stack in software development is crucial as it defines the combination of technologies used to build and run applications. This stack typically includes programming languages, frameworks, libraries, and tools for managing databases and servers. A well-chosen tech stack can impact a project's performance, scalability, and development speed. It also influences the team's skill set, as developers must be proficient with the selected technologies. Overall, the tech stack is fundamental in ensuring the success and maintainability of software solutions.