Package managers are libraries that allow developers to easily install, update, and manage software packages. They are commonly used in frontend development to quickly add libraries and frameworks such as React, Angular, or Vue. Package managers can be used to install packages from a repository or from a local directory. They also provide version control so that developers can easily switch between different versions of the same package. Additionally, they provide dependency management so that all the necessary dependencies for a package are installed automatically when it is added to the project.