This constant, `m_d *c^2`, defines the mass/energy equivalent of deuteron, the nucleus of Deuterium.  This mass energy equivalent of Deuteron is expressed in Mega electronvolts (MeV)

Notes

Deuterium (symbol D or 2H, also known as heavy hydrogen) is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in 6,420 of hydrogen.

This constant, `m_d`, is specified with a standard uncertainty (standard deviation) of: 0.000041 MeV