Definition
Non-defining attribute
A non-defining attribute can change without changing which shape class the figure belongs to.
What it means
These are changeable details, not entry rules. Turn a triangle, make it larger, or colour it green: it is still a triangle because its required shape properties have not changed.
Remember it
Change the detail; keep the shape name.
Example
Two rectangles are different sizes and colours, and one is tilted. Size, colour, and orientation are non-defining attributes of being a rectangle.
Watch for
Non-defining is relative to a class: equal side lengths are non-defining for triangles in general but defining for equilateral triangles.
Common mix-up
Non-defining does not mean invisible or unimportant; it means the feature is not required for membership in that class.
Exact meaning
A non-defining attribute of a shape class is a feature that can change while the figure remains a member of that class.