All properties are defined within a specific content model, which also defines a unique namespace. For example, a property called description can be part of many namespaces (content models). To uniquely identify what description property is being referenced, a fully qualified name, or a QName, is used. A QName has the following format: {namespace URL}property local name, for example:
{http://www.alfresco.org/model/content/1.0}description
The first part in curly braces is the namespace identifier defining the content model that the property is part of. The second part is the local name of the property (that is description in this case).
A QName is used for types, aspects, properties, associations, constraints and so on. The QName for the generic folder type that is part of the out-of-the-box document content model is cm:folder. Note the use of cm to denote the namespace. Each content model defines a prefix for each namespace that is used in the content model. Each type, aspect, property and so on in the content model definition uses the namespace prefix instead of the full namespace URL. You will also use the prefix when referring to entities such as types, aspects, properties, in the different APIs.