What is "hypothetical baptism"

Hypothetic \Hy`po*thet"ic\, Hypothetical \Hy`po*thet"ic*al\, a. Characterized by, or of the nature of, an hypothesis; conditional; assumed without proof, for the purpose of reasoning and deducing proof, or of accounting for some fact or phenomenon.

Causes hypothetical at least, if not real, for the various phenomena of the existence of which our experience informs us.
--Sir W. Hamilton.

Hypothetical baptism (Ch. of Eng.), baptism administered to persons in respect to whom it is doubtful whether they have or have not been baptized before.
--Hook. -- Hy`po*thet"ic*al*ly, adv.
--South.

n. (context religion English) Baptism administered to somebody who may or may not have been baptized before.