It refers to your own values, for example, if ,when you were young, your teachers told you that you were really bad at something, you may have believed it all thru' your life without challenging it and therefore that is a limiting belief.
Or, maybe you believed an old wives tale such as - if a baby bird has fallen from its nest, don't pick it up as its parent will reject it, smelling the human contact. This is not true but could influence you NOT to save a birds life, if ya see what i mean...
On the other hand, you may have been told something good about yourself which has encouraged you to continue in that manner - that is NOT a limiting belief.
Hope this helps....