List environments like itemize can be customized.

Itemize with small item spacing:

\item ITEM1
\item ITEM2

All available lengths

Length Description
\topsep Vertival space before and after list environment
\itemsep Vertical space between lines
\parsep Vertical space between paragraphs inside an item
\partopsep Vertical space before list environment if it starts a new paragraph

NOTE: You will not be able to modify topsep and partopsep inside a list environment because the space was already added at that point.

NOTE: The default values of these lengths depend on the depth of the list environment.

See Dense Lists for an example how to modify topsep and partopsep

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