What does polar and nonpolar mean in science

Polarity refers to the pull of electrons. Some elements like Fluorine and Oxygen pull electrons closer to them in their bonds (electronegativity), meaning they don't share them equally. So if they pull them closer, there is polarity in the molecule because there's a pull of electrons between atoms.

Polar molecules are molecules are essentially have no molecular symmetry.

Nonpolar molecules are molecules that have molecular symmetry.

Water is a very basic example of a polar molecule.