what does coefficients in equations mean, in chemical terms?

Question

2NaCl means we have two molecules or 2 mols of NaCl. Most texts caution us not to use molecules but to stick with the latter part of the definition (moles); however, I don't have any problem with saying,
2H2 + 2 O2 ==> 2 H2O
2 molecules of H2 will react with 2 molecules of O2 to produce 2 molecules of H2O. 2 mols of H2 will react with 2 mols O2 to produce 2 mols H2O.