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"?
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.
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.
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' 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 weren't actual "ghosts" but illusions created by the Son. Just as the image of Darth Bane Yoda faced on Moraband 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.
According to Wookiepedia:
Through special training, certain beings were able to appear as Force spirits through the Force.
So according to official canon wiki, they are known as Force Spirits or Force Ghosts.