Small Text. Specifically, 10pt.
Arno Pro comes in 5 optical weights: Caption, Small Text, Regular,
Subhead, and Display.
See:
http://www.adobe.com/type/topics/opticalsize.html
for a general description of optical weights.
T. Phinney, in http://blogs.adobe.com/typblography/2007/04/arno.html
states:
"For Arno, we minted a new size name of 'small text' in between
'caption' and 'regular,' for the 10 pt optical size."
Read the whole article for interesting background information and
links to more detail.
- Herb