If a villager moves out without being prompted to go to a particular town before they leave, they're in the void. If you have a void villager, they will move to the next town you connect to that has less than 10 villagers. OP doesn't want to accidentally drop off a villager when visiting someone with less than 10 that might not want the villagers they have in the void. The void is cleared when you visit a town with 10 villagers.
Edit: Void villagers also move to towns over Streetpass. Ugh, that's how I got Rocket haha
Just mean to be a little heads up. Actually visiting a town with 10 villagers (or hosting with them) clearing the void is wrong lore that's spreaded out to be common.
Thanks for the info! I knew the process but not the terminology - I swear I still learn new things about this game all the time and I've been playing since the day it came out!
ive gotten a villager from the void before he came the day after i got rid of someone, so i dont think the 10 villager strat works, or it just failed me haha, anyways, good luck!