So from the previews from the following episodes we get to know that

(spoilers)

> 
>  18 and 17 donates energy to Goku's Genki Dama. People speculated that since they have unlimited energy, Goku could get to form an extremely powerful Genki Dama thanks to their energy but no, because it's been said by some fans that ki energy (attack energy) is different than Genki energy Goku uses for the Genki Dama bomb.
> 
> 
> 

So what does Genki (from Genki Dama) mean?