FWIW, and this may be a silly answer...
A section, to me, would be an entire numbered section, i.e. Section 7, Product Realization.
A clause would be a subsection, such as 7.2.1 ("The organization shall determine...") "c) statutory and regulatory requirements..."
An element... how about aluminum? Seriously, "element" to me is vague, and could mean either of the above.