Wiktionary
n. (label en fandom slang) A person with whom one shares a profound spiritual bond; a soulmate.
Wikipedia
Imzadi is a non-canon Star Trek novel by Peter David, primarily exploring William Riker's assignment to Betazed and his early relationship with Deanna Troi.
Imzadi has a complex structure, involving time travel through the Guardian of Forever, but a straightforward plot of love and rescue. Troi's history with Riker had been introduced in the pilot episode of Star Trek: The Next Generation, " Encounter at Farpoint"; this also included the word imzadi, a Betazoid term of endearment usually translated as "beloved". The novel expands on the meaning of imzadi when Troi explains that its literal meaning is "the first," not necessarily referring to the first sexual partner but, as Troi puts it to Riker, "the first to ever touch your soul."
Usage examples of "imzadi".
Nothing…except the way that he had once again bungled his relationship with his Imzadi, with his Deanna.
Everything that went wrong with the relationship…everything that I screwed up, and it was me, Imzadi, I admit it, it was me…happened after the Falls.
Only his Imzadi seemed immune, lifting herself above the stupid bickering.
It was just like his Imzadi to befriend the Bajoran, thus gaining control over her.