Definition of "onto"

onto

/ˈɒn.tuː/

preposition
1. Arriving upon or on top of (speaking of a physical or metaphorical movement).
  Quotations
  Private-equity nabobs bristle at being dubbed mere financiers. Piling debt onto companies’ balance-sheets is only a small part of what leveraged buy-outs are about, they insist. Improving the workings of the businesses they take over is just as core to their calling, if not more so. Much of their pleading is public-relations bluster.
  2013 June 22, “Engineers of a different kind”, in The Economist, volume 407, number 8841, page 70
2. (informal) Aware of.
3. (mathematics) Being an onto function with a codomain of (see below).
adjective
not comparable
1. (mathematics, of a function) Assuming each of the values in its codomain; having its range equal to its codomain.