What would a 0.12M solution of an acid that ionizes only slightly in solution be termed?
Regardless of its concentration, it is called a weak electrolyte. Weak electrolytes dissociate slightly in solution, i.e. they form few ions in solution for a given sample of solute.
(We thus expect the conductivity of this solution to be low.)
Since it is an acid, it is also a weak acid.
We thus describe this small dissociation, or ionization, using the acid dissociation constant,
#K_a = (["A"^(-)]["H"^(+)])/(["HA"])#
for the reaction
#"HA"(aq) rightleftharpoons "A"^(-)(aq) + "H"^(+)(aq)#,
and for weak acids,