  We recall and update, both theoretically and phenomenologically, our (nearly)
forty-years-old proposal of a string-junction as a necessary complement to the
conventional classification of hadrons based just on their quark-antiquark
constituents. In that proposal single (though in general metastable) hadronic
states are associated with "irreducible" gauge-invariant operators consisting
of Wilson lines (visualized as strings of color flux tubes) that may either end
on a quark or an antiquark, or annihilate in triplets at a junction $J$ or an
anti-junction $\bar{J}$. For the junction-free sector (ordinary $q\, \bar{q}$
mesons and glueballs) the picture is supported by large-$N$ (number of colors)
considerations as well as by a lattice strong-coupling expansion. Both imply
the famous OZI rule suppressing quark-antiquark annihilation diagrams. For
hadrons with $J$ and/or $\bar{J}$ constituents the same expansions support our
proposal, including its generalization of the OZI rule to the suppression of
$J-\bar{J}$ annihilation diagrams. Such a rule implies that hadrons with
junctions are "mesophobic" and thus unusually narrow if they are below
threshold for decaying into as many baryons as their total number of junctions
(two for a tetraquark, three for a pentaquark). Experimental support for our
claim, based on the observation that narrow multiquark states typically lie
below (well above) the relevant baryonic (mesonic) thresholds, will be
presented.
