In chemistry, a polar molecule is one that has concentrations of positive or negative electric charge. Polar compounds are soluble only in other polar compounds.
A commonly-used example of a polar compound is water (H2O). The electrons of water's hydrogen atoms are strongly attracted to the oxygen atom, and are actually closer to oyxgen's nucleus than to the hydrogen nuclei; thus, water has a relatively strong negative charge in the middle, and a positive charge at the ends.
O H H <--- a water molecule