filtrate

A filtrate is the liquid, and sometimes the gas, that has passed through a filter. In filtration, you start with a mixture and end up with two parts: the material that stays on the filter and the filtrate that passes through it.

You will often see the word in science, medicine, and industry. In a laboratory, a chemist may filter a cloudy mixture and then study the filtrate, which is the clearer part collected below. In the body, the kidneys produce what is called glomerular filtrate, an early stage in the process of cleaning the blood. Water treatment works in a similar way, because water may pass through sand, charcoal, or other materials before the cleaned liquid moves on.

The verb form filtrate exists, but it is much less common than filter and is mainly used in technical contexts. In everyday English, people usually say they filter water, coffee, air, or a solution, and then refer to the liquid that comes through as the filtrate. So the central idea is simple: something passes through a filter, something else is left behind, and the part that gets through is the filtrate.