Baravelle spirals are generated by connecting the midpoints of the successive sides of a regular polygon. Triangles will be formed. The process of identifying and repeatedly connecting the midpoints is called iteration.
Spirals are curved lines that grow bigger and bigger from the center.
I don't know how to relate your question specifically to arts and crafts without further information.
A spiral galaxy is a "spiral" without a physical bar structure. Whereas a barred spiral galaxy has an obvious central bar. See related pictorial for a better idea.