Okay kiddo, do you know what happens when you mix water and dirt together? The dirt dissolves in the water and becomes part of it, right? Well, when you mix two things together and one of them dissolves the other, we call the thing that does the dissolving the "solvent".
Think of it like a superhero! Just like how Superman has special powers that let him save people, solvents have special powers that let them dissolve things.
Some common solvents you might have heard of before are water, alcohol, and acetone (which is what's in nail polish remover).
So basically, a solvent is something that helps things dissolve, kind of like how soap helps you clean your hands. Pretty neat, huh?