A "darling" is any element of your work that you keep out of vanity rather than necessity. Common examples include: Killing Your Darlings - A Writer's Journey
While frequently attributed to William Faulkner or Stephen King, the phrase originated with in his 1916 book, On the Art of Writing . Quiller-Couch famously wrote: Kill Your Darlings
"Whenever you feel an impulse to perpetrate a piece of exceptionally fine writing, obey it—whole-heartedly—and delete it before sending your manuscript to press. Murder your darlings." A "darling" is any element of your work