Tetraquark states are composed of four quarks and represent
a type of exotic hadronic state that extends beyond the conventional
quark model of two-quark mesons and three-quark baryons.
In this review, we summarize the experimental advances in the study of
tetraquark states, highlighting various configurations of quark flavors.
We show the lineshape measurement of the $\x$, observation of
charged quarkonium states consisting of a heavy quark-antiquark pair
alongside a light quark-antiquark pair, discoveries of tetraquark states
with four distinct flavors, with a pair of heavy quarks and
a pair of light anti-quarks, or with two-pairs of charm-anticharm quarks.