  This talk briefly discusses the set of meson resonances discovered in the
latest decade. They are frequently treated in the literature as tetraquarks or
hadron molecules. Our consideration (using the energy-time uncertainty
relation) suggests, however, that the most reasonable description for each of
them may be a two- (or more-) component Fock column, with one line being a
conventional quark-antiquark pair, and the other line(s) corresponding to a
charmed (or beauty) meson-antimeson pair near its threshold. Detailed
investigation of decay properties might allow to reveal presence of several
Fock components and separate their contributions.
