The Book of the Dead is the common name for the collection of ancient Egyptian funerary texts known as The Book of Coming [or Going] Forth By Day. The title "Book of the Dead" was created by German Egyptologist Karl Richard Lepsius, who was the first to published a selection of the ancient texts in 1842.
The word “book” is a misnomer as the Egyptian texts were carved on the exteriors of the deceased person's sarcophagus. Later the texts were written on papyrus scrolls and buried inside the sarcophagus along with the deceased, presumably so that may be utilized in the afterlife/
In sarcophagi uncovered over the last hundred or so years other shorter texts called hypocephalus (meaning 'under the head') which were primer versions of the full texts were discovered too.
The so called Books of the Dead are a collection of spells, charms, magical passwords, and formulas that are to be used by the deceased in the afterlife. In these scrolls the basic stories of ancient Egyptian mythology are alluded to. They are written as guides to the afterlife and to explain the tribulations the dead will encounter on the road to the underworld. In describing the stories of the gods, the dead are given clues to the way to pass certain hurdles.
Knowledge of the appropriate spells was considered essential to achieving contentment after death. Each sarcophagus was given a unique set of spells which reflected the class, prominence, and personality of the specific dead person. While many of these Books of the Dead had commonalities they also had a wide variety of specific verses and spells.
The Books were usually lavishly illustrated, graphically describing the deceased’s impending tests, the most of which was the weighing of the heart of the dead person against Ma'at, or Truth. Carried out by the god of the dead Anubis, the deceased’s heart of was weighed against a feather--if the heart was not weighed down with sin it was lighter than the feather and the dead was allowed to move on. The god Thoth would record the results and the monster Ammit would wait nearby to eat the heart should it prove unworthy.
The earliest known versions date from the 16th century BCE during the 18th Dynasty (ca. 1580 BCE–1350 BCE). These versions incorporated earlier prayer texts, known as the Coffin Texts (ca. 2000 BCE) and the Pyramid Texts (ca. 2600 BCE-2300 BCE).
While no two ancient versions of the Book of the Dead are the same, the modern text version is based on four basic texts.