Nearly all the code you write in Dart will be contained in classes. And a class is a blueprint for an object. That is, a class describes an object that you can create. The object itself is what holds any specific data and logic. For example, a Cat class might look like this:

class Cat {
    String name;
    String color;
}

The variable declarations above, String name and String color, are called properties or class members. (NB: Members can also refer to functions, getters and setters on classes.)

Instances of classes

This class describes an object that can be created, like this:

Cat nora = new Cat(); // note: the `new` keyword is optional in Dart 2
nora.name = 'Nora';
nora.color = 'Orange';

class Cat {
    String name;
    String color;
}
void main() {
    var nora = Cat();
    nora.name = 'Nora';
    nora.color = 'Orange';
    print(nora);
    print(nora.name);
    print(nora.color);
}