Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek word παράλλαξις (parallaxis), meaning "alteration". Due to foreshortening, nearby objects have a larger parallax than more distant objects when observed from different positions, so parallax can be used to determine distances.

Vampire literature covers the spectrum of literary work concerned principally with the subject of vampires. The literary vampire first appeared in 18th century poetry, before becoming one of the stock figures of gothic fiction with the publication of Polidori's The Vampyre (1819), which was inspired by the life and legend of Lord Byron. Later influential works include the penny dreadful Varney the Vampire (1847); Sheridan Le Fanu's tale of a lesbian vampire, Carmilla (1872) and the masterpiece of the genre: Bram Stoker's Dracula (1897). In the meantime some authors created a more "sympathetic vampire" and in particular Anne Rice's novel Interview with the Vampire has received recognition as a turningpoint.