Light crude oil is liquid petroleum that has a low density and flows freely at room temperature. It has a low viscosity, low specific gravity and high API gravity due to the presence of a high proportion of light hydrocarbon fractions.
Rather than referring to weight, they actually refer to density, with “light” crude being less dense than heavy crude. Light crude has a low viscosity and because it has low wax content, it is a liquid at room temperature. These properties make it easy to pump and extract.