y is by default interpreted as DoubleVerticalBar[x,y]. Used in mathematics to indicate that x exactly divides y. Used in geometry to mean "parallel to". Not the same as \[LeftDoubleBracketingBar], \[RightDoubleBracketingBar]. || is the alias for \[Or]. The alias for \[DoubleVerticalBar] has a space at the beginning. See The Mathematica Book: Section 3.10.4. See also: \[VerticalBar], \[VerticalSeparator], \[NotDoubleVerticalBar].