Fredholm Integral Equation
Definition1
The integral equation given below is called the Fredholm Integral Equation of the first kind.
$$ g(s) = \int K(s, t) f(t) dt \tag{1} $$
Here, $K$ is referred to as the kernel. The following form is called the Fredholm Integral Equation of the second kind.
$$ g(s) = f(s) + \int K(s, t) f(t) dt \tag{2} $$
Explanation
Solving the integral equation $(1), (2)$ generally means finding $f$ that satisfies $(1), (2)$ for given $g$ and $K$.
Erwin Kreyszig, Introductory Functional Analysis with Applications (1978), p319 ↩︎