A maintainer is a developer who oversees the ongoing development and stability of a software project. They are responsible for reviewing, approving, and integrating changes or updates submitted by other contributors. Maintainers ensure that the project's code remains reliable, secure, and aligned with its goals. In open-source projects, maintainers play a key role in managing contributions, resolving issues, and guiding the project's direction. Their work helps keep software up to date, secure, and useful for its users.