Bazel is a build tool developed by Google that is used for building and testing software projects. It enables developers to build large, complex software projects more efficiently by providing a scalable, distributed system for building, testing, and deploying code. Bazel uses a build specification language called Starlark and supports multiple programming languages, including Java, C++, Python, and Go. It also supports caching and incremental builds, which leads to faster build times and better productivity.