What are the different ways that a political candidate can become nominated?

I know 3 of the ways, but I'm a little lost on the 4th one. The 3 ways I know for sure are by: Caucuses, Pettitions, and Primaries.

If anyone knows the 4th, I'd be thankful, lol.

-R in CA

there's five ways self announcement, petition, caucus, convention and direct primary