Noun
English Wikipedia has an article on:Bessel functionWikipedia
Bessel function (plural Bessel functions)
(mathematics) Any of a class of functions that are solutions to a particular form of differential equation (a Bessel equation) and are typically used to describe waves in a cylindrically symmetric system.
The Bessel function of the second kind then can be thought to naturally appear as the imaginary part of the Hankel functions. Source: Internet
In 1764, Euler examined the partial differential equation for the vibration of a circular drum and found one of the Bessel function solutions. Source: Internet
The Bessel function of the first kind is an entire function if α is an integer, otherwise it is a multivalued function with singularity at zero. Source: Internet
In this case, the second linearly independent solution is then found to be the Bessel function of the second kind, as discussed below. Source: Internet