In Integration notation, much like differentiation notation, the most commonly used notation form is Leibniz's notation.
If you are working with multiple variables see multiple integral notation for additional information.
Named after Gottfried Leibniz, the Leibniz Notation is the most common and likely the one you are most familiar with. Integrals of a function
The above integral on the left is an indefinite integral while the one on the right is a definite integral where the bounds of the definite-integral are given by