What is a neat liquid?

Hint: A liquid is a virtually incompressible fluid that conforms to its container's shape while maintaining a constant volume regardless of pressure. It is thus one of the four fundamental states of matter (the others being solid, gas, and plasma) and the only one with a definite volume but no fixed form.

Complete step-by-step answer:
If a liquid is a pure substance (a single compound or element) in the liquid phase, it is said to be "neat."
Pure anhydrous ethanol, for example, is a "neat liquid." Pure benzene, like pure water, is a "neat liquid" with nothing added to it.

However, the following are not "neat" which means they don’t have a single compound or element
(a) vodka (basically a combination of ethanol and water)
(b) motor oil (which includes a variety of molecular types)
(c) the aqueous solution (which contains water and other dissolved substances).

Additional Information:
- Pure liquids and liquid mixtures are the two broad types of liquids.
- Liquids are almost impervious to compression. Molecules in liquids are very similar to one another. There isn't a lot of space between the molecules. The molecules are unable to be pressed closer together.
- In normal circumstances, liquids have boiling points that are higher than room temperature. As liquids are heated, they gradually transition to a vapour or gaseous state.

Note: 'Neat' loosely translates to 'pure.' We are just concerned with the reactants when we run a reaction neat; there's no solvent or catalysts or initiators involved. A solvent may be one of the reactants, or it could be a solid-state or gas or plasma-phase reaction. Chemicals such as acetic acid or hydrogen peroxide are often watered down.