The squiggly line is called a tilde. It is a typographical symbol that resembles a wavy line and is used in a wide range of IT-related applications, math, computer programming, and to form certain letters in Spanish and Portuguese. In Spanish, it is called "virgulilla" and can be used to indicate a change in sign or an approximation of a value. In English, it has no accepted usage in formal writing, but it may occasionally be used for a few different reasons in informal writing.