In chemistry, polarity refers to a separation of electric charge leading to a molecule having an electric dipole (a separation of positive and negative charge). Polar molecules can bond together due to dipole–dipole intermolecular forces between one molecule (or part of a large molecule) with asymmetrical charge distribution and another molecule also with asymmetrical charge distribution. Molecular polarity is dependent on the difference in electronegativity (the ability of an atom to attract electrons towards itself in a covalent bond) between atoms in a compound and the asymmetry of the compound's structure. For example, a molecule of water is polar because of the unequal sharing of its electrons in a "bent" structure, whereas methane (CH4) is considered non-polar because the carbon shares the electrons with the hydrogen atoms uniformly. Polarity underlies a number of physical properties including surface tension, solubility, and melting- and boiling-points.
For more, visit the Wikipedia entry for aqueous solution, URL: http://en.wikipedia.org/wiki/Chemical_polarity