horcrux
In Harry Potter, an object in which a wizard has concealed a part of their soul through magic, rendering them immortal until the object is irreparably damaged or destroyed.
They stared at it as if it was the one ring or the holy grail or a horcrux, or perhaps all of them rolled into one. An empty, plastic cat food bowl.
Something in which one has invested a part of one's self; an object which allows for the preservation of memory, culture, etc.
When I read manuscripts, I feel very aware that some part of the writer's soul lives in the pages—like a good Horcrux, say—and if I’m turning one down, I need to do so with thoughtfulness and respect.
Where it comes from
Coined by author J. K. Rowling apparently at random; "invent[ed] […] after much transposition of syllables". Fans have pointed to the possible influence of Middle English hore (“iniquity, evil, sin”) and English crux (“the central or essential part”), or Turkish hortlak (“ghost”) among other theories. The term first appears in Harry Potter and the Half-Blood Prince (2005).
Adapted from the Wiktionary entry horcrux (CC BY-SA 4.0).