Unequal sharing occurs when one atom is more than another

In summary, a polar bond results when different atoms share electrons. One atom will attract the bonding electrons more strongly than the other atom and will acquire more than a half share of these electrons. This leaves the other atom with less than a half share and makes the electron distribution unsymmetrical. On a time-average basis the electrons spending more time with one atom and cause it to have a partial negative charge. The other atom, deficient in electrons, acquires a partial positive charge.

it is the most commonly accepted one