\tilde{a}The tilde accent is used to place a tilde (~) over a letter, often used in mathematics and physics to denote an approximation, a related quantity, or a different state of a variable.
Indicating that 'a' is approximately equal to 5.
\tilde{a} \approx 5A modified or related state of the wave function \psi.
\tilde{\psi}Representing a perturbed or adjusted velocity.
\tilde{v} = v + \delta v