Unreproducible Bug
Noun · Hacker Culture
Definitions
A bug that is known to exist from reports or evidence but cannot be consistently reproduced on demand, making diagnosis and fix validation difficult. These bugs are especially painful because they sit between anecdote and proof.
In plain English: A bug people know is real but cannot reliably make happen again in testing.
Example: "The mobile crash is an unreproducible bug so far; we only have two field traces and no stable local repro."