It's the inverse of the Fine Structure Constant, which gives the strength of
the interaction of charged particles via photon exchange. It interrelates the
speed of light, the relative masses of the electron and the neutron, and
Planck's constant. It has no units. It's very close to 1/137. It's
intimately tied up with the study of the Higgs boson. It's used by physicists,
numerologists and spinning woo-li boogers to prove all sorts of silly things,
decide whether the speed of light is constant, and so on. It's something you
should know about.
Cheers,
Wayne
Don't waste a lot of time on this, but here're a few references:
http://hepwww.ph.qmw.ac.uk/epp/lectures/lecture13/lecture13.html
http://www.ldolphin.org/cdkconseq.html
http://dgleahy.com/dgl/p13.html
http://www.ptb.de/english/infos/publicat/ptb-news/news2611.htm
http://www.hookup.net/~jrlawson/part_4.html