Visibility

Visibility applies to attributes or operations, and specifies the extent to which other classes can use a given class's attributes or operations.

Three levels of visibility are possible (last symbols are used in UML classes to indicate different levels of visibility):
public level usability extends to other classes

+

protected level usability is open only to classes that inherit from original class #
private level only the original class can use the attribute or operation -
visibility Public and private operations in a HardDisk