Question: I realize that, out-of-universe, we have come to refer to them as Force Ghosts. However I doubt Qui-Gon or Yoda would use the words "Force Ghost" to describe what happens. Is there an **in-universe** word or phraseology that Jedi would use to refer to what we call "Force Ghosts"?

Answer: 
If I am allowed to go by *Legends* sources in answering your question, then it appears that at least a few characters did, in fact, refer to them simply as "Force Ghosts." Here's a conversation between Ordith Huarr and Jedi Knight Nelani Dinn, excerpted from the novel *Legacy of the Force: Betrayal*:

> 
> "What is a Force ghost?" Huarr asked. Nelani was silent for a long moment. "It's a survival, a sending from someone who has died but still exists in a certain way..."
> 
> 
> 

However, there are other *Legends* sources where characters seem to show some disagreement with that term, as shown in this excerpt from *Luke Skywalker and the Shadows of Mindor*:

> 
> "Sometimes, things not going according to plan is a *gift,*" Han said. "You gotta go with the flow, y'know? I mean, trust in the Force, right? Would the Force have brought you this chance if you weren't supposed to take it?"
> 
> 
> "I don't know," Luke admitted.
> 
> 
> **"Why don't you ask Kenobi himself, the next time he shows up with that Force-ghost thing of his?"**
> 
> 
> **"He's not a *ghost--*"**
> 
> 
> **"Whatever. You know what I mean."**
> 
> 
> 

If you would rather have a *Canon* source, then I'm afraid that I'm not certain if any currently available *Canon* sources have yet provided any examples of a character referring to them by name. *Wookieepedia* refers to them as "Force spirits," if you find any value in that, but I was unsuccessful in my attempt to find excerpts of any characters using that term.
So far in canon, no, there doesn't appear to be a specific term. They're only referenced as one would an individual. Mostly, they're not referenced at all in dialogue.

This would actually make sense since unlike in Legends, this is not a common enough phenomenon in canon for it to be discussed frequently enough to warrant a specific term. Until Qui-Gon contected Yoda in '[Voices](https://starwars.fandom.com/wiki/Voices)' it was thought impossible for someone to retain their individuality and return from the "netherworld of the force."

Even the visions of Qui-gon, Shmi and grown-up Ahsoka on [Mortis](https://starwars.fandom.com/wiki/Overlords) weren't actual "ghosts" but illusions created by the Son. Just as the [image of Darth Bane Yoda faced on Moraband](https://starwars.fandom.com/wiki/Sacrifice) was an illusion created by the Force Priestesses, who where themselves apparently actual force ghosts, though far more solid looking than we saw in tESB and RotJ.

**Addendum**: Since I gave the initial answer some more information has come to light. While it does not change anything substantive, it may add more context and indeed demonstrate that the term "ghost" may not be appropriate even out of universe. Perhaps most significantly is the short story '[Master and Apprentice](https://starwars.fandom.com/wiki/Master_and_Apprentice_(short_story))' by Claudia Gray (not to be confused with the [novel of the same name](https://starwars.fandom.com/wiki/Master_&_Apprentice), also by Gray.) In which the story is told entirely from Qui-Gon's perspective as he manifests a physical form to communicate with Obi-Wan during the events of ANH (specifically, at the Sandcrawler after Luke rushed off home.)
The key phrase there is "physical" form. Flesh, blood and bones and all; so it seems the term "ghost" isn't even apt since they're not just projections or apparitions but actual tangible (if temporary) bodies.

This actually lines up quite well with depictions in RotJ, TLJ and other more recent stories which I shall not spoil. In which transcendent force users are seen to interact with people and objects; in the former case Kenobi is seen moving vines aside before sitting down on a log, while in the latter Yoda bops Luke on the nose with his walking stick.