The noun abyss refers to a deep void or chasm — either literal or figurative. Making a momentous life decision with great uncertainty, like enrolling in clown college, might feel like jumping into the abyss.
Traditionally, the abyss referred to the "bottomless pit" of Hell. Now it might refer to either a literal chasm or a figurative one: "Thirty years ago, we peered into this abyss and pulled back just in time." The word is sometimes used to describe a wide difference between cultures or nations. Abyss comes from Greek: a- "without" + byssos, "depth, bottom." You may know the related adjective abysmal, which means "appallingly bad" — or "way down in the depths," as it were.