The tilde is the mark "~" placed on top of a symbol to indicate some special property. is voiced "-tilde." The tilde symbol is commonly used to denote an operator. In informal usage, "tilde" is often instead voiced as "twiddle" (Derbyshire 2004, p. 45).
1. An operator such as the differential operator .
2. The statistical median (Kenney and Keeping 1962, p. 211).
The tilde is sometimes used as its own symbol.
1. In asymptotic notation, is used to mean that .
2. Physicists and astronomers use same notation to mean " is of the same order of magnitude as ."
3. In set theory, means that there is an equivalence relation between and .
4. In statistics, the tilde is frequently used to mean "has the distribution (of)," for instance, means "the stochastic (random) variable has the distribution (the standard normal distribution). If and are stochastic variables then means " has the same distribution as .