What is "initiate tenant by courtesy"

Initiate \In*i"ti*ate\, a. [L. initiatus, p. p.]

1. Unpracticed; untried; new. [Obs.] ``The initiate fear that wants hard use.''
   --Shak.

2. Begun; commenced; introduced to, or instructed in, the rudiments; newly admitted.

   To rise in science as in bliss, Initiate in the secrets of the skies.
   --Young.

   Initiate tenant by courtesy (Law), said of a husband who becomes such in his wife's estate of inheritance by the birth of a child, but whose estate is not consummated till the death of the wife.
   --Mozley & W.