In Go, a package is a way to organize and reuse code. A package is a collection of Go source files that are organized together in a directory. Each package can contain multiple functions, variables, types, and constants that can be accessed from other packages or programs.

Go has two types of packages: built-in (also known as the standard library) and custom (also known as user-defined). Built-in packages are included in the Go installation and provide a set of commonly used functions and types. Custom packages are created by the user to organize and reuse their own code.

To use a package in your Go code, you must first import it using the import statement. Once imported, you can access the exported functions, variables, types, and constants from the package by prefixing them with the package name.

Go's package system also allows for package-level documentation, making it easier for developers to understand how to use and interact with the code within a package. Additionally, Go's package system supports versioning, which enables developers to use different versions of a package in their projects without fear of conflicts.

Overall, Go's package system is a powerful tool for organizing and reusing code, which can help developers write cleaner, more maintainable, and more scalable software.