«والمقيد: ما يدل على الذات مع خصوص صفاتها»
A restricted expression denotes the thing together with its specified attributes.
“Pen” names the object; “blue pen” adds colour as a requirement. Pens lacking that attribute no longer satisfy the latter request.
In muqayyad, the underlying object is not replaced. The range of objects that satisfy the wording is narrowed by a relevant qualification.