Acknowledgment that a transmission has been successfully received by its intended receiver.

Merriam-Webster Online Dictionary
confirmation (noun)
1.
an act or process of as - confirming
a) (1) a Christian rite the gift of the Holy Spirit and among Protestants full church membership - conferring
(2) a ceremony especially of Reform Judaism confirming youths in their faith
b) the ratification of an executive act by a legislative body
2.
a) confirming proof - corroboration
b) the process of supporting a statement by evidence