  We discuss the problem of how Majorana mass terms can be generated in
low-energy systems. We show that, while these terms imply the Majorana
condition, the opposite is not always true when more than one flavour is
involved. This is an important aspect for the low-energy realizations of the
Majorana mass terms exploiting superfluid pairings, because in this case the
Majorana condition is not implemented in the spinor space, but in an internal
(flavour) space. Moreover, these mass terms generally involve opposite
effective chiralities, similarly to a Dirac mass term. The net effect of these
features is that the Majorana condition does not imply a Majorana mass term.
Accordingly the obtained Majorana spinors, as well as the resulting symmetry
breaking pattern and low-energy spectrum, are qualitatively different from the
ones known in particle physics. This result has important phenomenological
consequences, e.g. implies that these mass terms are unsuitable to induce an
effective see-saw mechanism, proposed to give mass to neutrinos. Finally, we
introduce and discuss schemes based on space-dependent pairings with nonzero
total momentum to illustrate how genuine Majorana mass terms may emerge in
low-energy quantum systems.
