An ovule can be defined as:
a. a female gametophyte that has developed within a sporangium that has dispersed with the aid of additional protective sporophyte tissue layers.
b. a sporangia protected by sporophyte tissue layers and containing a single non-dispersed spore that has developed into a female gametophyte.

A

female gametophyte that has developed within a sporangium that has dispersed with the aid of additional protective sporophyte tissue layers

Explanation: An Ovule is made up of three parts: The integument, forming its outer layer, the nucellus (or remnant of the megasporangium), and the female gametophyte (formed from a haploid megaspore) in its center.

It is the structure that gives rise to and contains the female reproductive cells in seed plants.