A DataMember, also InstanceVariable or ivar, is a data variable which is a part of AnObject.
It can be many things, from something as simple as an integer:
Through more complex things like strings:
Up to complex things like selectors:
And advanced things like objects:
id someObject; NSString * stringObject;
A DataMember is sometimes also referred to as an InstanceVariable (or “ivar” for short) because it is a variable that only exists within an instance of a class.