Some of you have questions so I will answer them. 

1) What is an altean?

This is the internet version: Alteans are an alien race native to planet Altea and previously ruled by King Alfor. They were once thought extinct, with Allura and Coran as the sole survivors. However, Haggar and her son Lotor are both revealed to be Altean. Furthermore; a thriving colony of Alteans are discovered hidden inside the Quantum Abyss, preserved for Lotor's devious purposes.

But you would only know that if you were to watch the show. Yes, there is a show. It is called,"Voltron: Legendary Defenders.

But in here:

Alteans are what Allura and Coran are. They are(or that is what they thought) known to be the last two alteans left. But nope, there is more of them. And since they are the only alteans left since Zarkon destroyed their planet, for Lance to see the light is impossible unless he was an altean. And he aint. The only alteans are Coran and Allura.(except gybvgyjbvg: find out in the show! :3)

That is basically it. Without explaining further and basically spoiling. Also i got the information from this: https://voltron.fandom.com/wiki/Altean