The act of dipping or plunging the subject into the water used in the administration of Baptism; called triple or trine immersion when the candidate is dipped three times, in the name of each Person of the Holy Trinity.
Immersion was the method generally employed in the early Church.
The Greeks still retain it; but though valid, for obvious reasons immersion has practically become obsolete in the Latin Church.
It is practised by Brethren (Dunkers) and other religious bodies in America.
New Catholic Dictionary