explain Depletion-mode MOSFET, Enhancement type MOSFET

With an appropriate voltage applied between source and drain, current will flow through the channel, as a semiconductor resistance. However, if we now apply a negative voltage to the gate, as shown to the right, it will amount to a small negative static charge on the gate. This negative voltage will repel electrons, with their negative charge, away from the gate. But free electrons are the majority current carriers in the n-type silicon channel. By repelling them away from the gate region, the applied gate voltage creates a depletion region around the gate area, thus restricting the usable width of the channel just as the pn junction did.
Because this type of FET operates by creating a depletion region within an existing channel, it is called a depletion-mode MOSFET.