Absolute delivery of deed

What does Absolute delivery of deed mean in American Law?

The definition of Absolute delivery of deed in the law of the United States, as defined by the lexicographer Arthur Leff in his legal dictionary is:

Actual manual delivery of a deed, with intention of giving up all rights in the deeded property and vesting them in the grantee. The hand delivery part seems to have little modern legal significance; mailing the deed with the same intent would seem to have the same effect as a hand-to-hand transmission.