Yes, it is easy to see that nearly six years of magical education have not been wasted on you, Potter. Ghosts are transparent.Severus Snape in Harry Potter and the Half-Blood Prince
Monsters are real, and ghosts are real too. They live inside us, and sometimes, they win.MonstersStephen King
True love is like ghosts, which everyone talks about and few have seen.LoveFrançois de La Rochefoucauld
More ghosts have been created in bedrooms than anywhere else.Jonathan Stroud in Lockwood & Co. - 4: The Creeping Shadow
My roommates are convinced our house is haunted.
I've lived here for 380 years and can confirm that nothing unusual is happening.
Harry: "If I dropped dead every time that old bat said I would, I'd be a medical miracle."
Ron: "You'd be some sort of extra-concentrated ghost."
Monsters are real. Ghosts are too. They live inside of us, and sometimes, they win.MonstersStephen King in The Shining
You can call them ghosts, if you'd like, or as I like to call them, "the living-impaired".Casper the Friendly Ghost, by Dr. James Harvey