An annotation is metadata—data about data. An annotation is a way to keep additional information about the code in the code itself. An annotation can have parameter values to pass specific information about an annotated member. An annotation without parameters is called a marker annotation. The purpose of a marker annotation is just to mark the annotated member.
Dart annotations are constant expressions beginning with the @ character. We can apply annotations to all the members of the Dart language, excluding comments and annotations themselves. Annotations can be:
Interpreted statically by parsing the program and evaluating the constants via a suitable interpreter
Retrieved via reflection at runtime by a framework