Similar types of classes, interfaces, and sub-packages are known as packages in Flutter or any other object-oriented language. The packages and plugins are used in development to reduce the coder's effort. The coder need not write the code for everything and can use packages and plugins to reduce the coding effort.
The distinction between packages and plugins is minute. Packages are new components or written code in Dart language. Plugins, on the other hand, use native code to allow more functionality. Sometimes the two terms are confused as the same, but a minute distinction exists.