  Type-III seesaw is a simple extension of the Standard Model~(SM) with the
SU$(2)_\text{L}$ triplet fermion with zero hypercharge. It can explain the
origin of the tiny neutrino mass and flavor mixing. After the electroweak
symmetry breaking the light neutrino mass is generated by the seesaw mechanism
which further ensures the mixings between the light neutrino and heavy neutral
lepton mass eigenstates. If the triplet fermions are around the electroweak
scale having sizable mixings with the SM sector allowed by the correct gauge
symmetry, they can be produced at the high energy colliders leaving a variety
of characteristic signatures. Based on a simple and concrete realizations of
the model we employ a general parametrization for the neutrino Dirac mass
matrix and perform a parameter scan to identify the allowed regions satisfying
the experimental constraints from the neutrino oscillation data, the
electroweak precision measurements and the lepton-flavor violating processes,
respectively considering the normal and inverted neutrino mass hierarchies.
These parameter regions can be probed at the different collider experiments.
