Liquid
Liquid means a substance or mixture of substances that flows readily, but, unlike a gas, does not expand indefinitely (i.e., a substance with constant volume but not constant shape). Liquid does not include powders or other materials that are composed entirely of solid particles.
Source
40 CFR § 59.202
Scoping language
The terms used in this subpart are defined in the Clean Air Act (Act) or in this section as follows: