Aqueous means containing water, made of water, or dissolved in water. Scientists use this word often when describing solutions: an aqueous solution is one where a substance has been dissolved in water, like salt water or sugar water.

When chemists write that something is in an aqueous state, they mean it's mixed with or surrounded by water.

You encounter aqueous solutions constantly, though you might not call them that: lemonade is an aqueous solution of sugar, lemon juice, and water. The blood flowing through your body is an aqueous solution carrying nutrients, oxygen, and other materials dissolved in water. Even the liquid inside your cells is aqueous.

In chemistry class, you'll see aqueous abbreviated as (aq) in chemical equations. When your textbook says “dissolve the salt in an aqueous medium,” it simply means dissolve it in water. The opposite of aqueous is anhydrous, meaning without water, though you'll hear that term less often.