Illustrated Glossary of Organic Chemistry

Neat: A sample or process which is conducted in a liquid phase, without any solvent. The term is probably borrowed from bartending, where 'neat' refers to a single (unmixed) liquor, served by itself on 'on the rocks' (over ice).

Octan-2-ol (neat)
Octan-2-ol (CCl4 solution)
Compare the infrared spectra of octan-2-ol (neat) versus 2-octanol (in CCl4 solution). Note the shape of the O-H stretching peak at ~ 3400 cm-1.

Whiskey, neat.
Whiskey, neat, rocks.