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*:

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> "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..."
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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*:

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> "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?"
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> "I don't know," Luke admitted.
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> **"Why don't you ask Kenobi himself, the next time he shows up with that Force-ghost thing of his?"**
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> **"He's not a *ghost--*"**
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> **"Whatever. You know what I mean."**
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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.
In *Specter of the Past*, Luke mentions to R2 his belief that a dying Jedi can "anchor" himself to a nearby Jedi, explaining how Obi-Wan stayed with him so long. He does not use a noun for the phenomenon.