Trilogy or Series?

Regarding my Killer Series. Here's the question. If I write only three books in the Killer Series, would that be considered a series or would it be considered a trilogy? A famous trilogy that comes to mind is the Lord of the Rings trilogy. Even with the release of the Hobbit, (which the movies made into another trilogy,) LOTR is still considered a trilogy.

The Bourne trilogy was a trilogy until the fourth Bourne movie came out. So now it's a franchise, which is another way to say a series. So I guess my killer series will be considered a trilogy until I write a fourth book. Then it will truly be a series. I suppose that means I'll be compelled to write that fourth book. Not so easily done considering I'm still in the beginning stages of Book Three.

And after Book Three? I have no clue where Trent Smith, the world's greatest martial artist will be. Where he'll go, or what he'll do. But that's the quandary of a series. You have to keep it fresh. Meaning you have to have new ideas, new characters, and new stories.

It reminds me of the show called Vikings. How many times will Ragnar's brother, Rolo, be languishing over his secondary role to his brother? How often will he be considering betraying him, as he's doing once again in season three. It's like every season we have to see Rolo kicking himself for not being as great as his brother, and considering betraying his brother to make himself great.

Sheesh, it's the same story over and over again. Don't get me wrong, I like that show. I like the characters, the plots, and the turn of events. I just wish Rolo would finally accept his place as "brother to the king" rather than harboring the sentiment, "Why can't I be as great as my brother the king?"

I mean, already Ragnar has granted Rolo mercy and spared his life for betraying him in season one. But ever since then, instead of being grateful for his life, he continues to question his own lack of greatness, and finding a reason to blame it on Ragnar.

Well, I can guarantee my Killer Series won't be anything like that. Still, it's a long way off. Got a lot of writing to do.