In chemistry, hydrochlorides are salts resulting, or regarded as resulting, from the reaction of hydrochloric acid with an organic base (mostly amine).
For example, reaction of pyridine (C5H5N) with hydrochloric acid (HCl) yields pyridine hydrochloride (C5H5N.HCl). Even though, this style of formulas is often used for denoting the hydrochlorides, the dot between both parts would mean it is 1:1 mixture, or two molecules weakly bonded together, which is not true. It is the salt C5H5NH+ Cl- with correct chemical name pyridinium chloride.
Converting otherwise water-insoluble amines into hydrochlorides is a common way to make them water-soluble. Many pharmaceutical substances are used as hydrochlorides.