Do algae have organs?

Algae are photosynthetic, eukaryotic organisms that do not develop multicellular sex organs. Algae can be single-celled, or they may be large and comprised of many cells.

Meaning it is undefined?

No. They have specialized male and female sex organs in which male and female gametes are produced respectively. Sex organs in the algae is unicellular and jacketless, Chara is an exception. Carpel is known as a female reproductive part present in angiospermic plants.