Vegetative propagation in mint occurs by

A sucker is a lateral branch that arises from the basal, underground portion of the main stem, grows horizontally beneath the soil for some distance and then comes out obliquely upward to give rise to a leafy shoot.
Suckers are found in mint, banana, pineapple and $Chrysanthemum$.
Runners are found in grass and strawberry, offsets in $Pistia$ and $Eichhornia$, and rhizomes in ginger and turmeric.
Hence vegetative propagation in mint occurs by suckers.