A tech stack refers to the collection of technologies used to develop an application or system, including languages, frameworks, and tools. It is crucial for development because it defines the architecture and workflow of the project. The choice of a tech stack can influence a project's scalability, performance, and long-term maintenance. A well-chosen tech stack aligns with developer skill sets and project objectives, facilitating efficient collaboration and expedited development cycles. Being aware of emerging technologies can also help teams stay competitive and innovative.