private

In short: private makes an element visible only inside its own class.

In more detail: Other classes, including subclasses, cannot access it. This keeps the internal representation hidden (encapsulation).

In Depth

public class Account {
    private double balance;
    public double getBalance() { return balance; }
}

Constructors can also be private, for example in the singleton pattern. See access modifiers, getter, setter.

See also: Access Modifiers, public, protected, Getter