What are polar covalent compounds?

A bond between 2 non-metal atoms that have different electronegativities and therefore have unequal sharing of the bonding electron pair is a polar covalent bond.
Example: In H-Cl, the electronegativity of the Cl atom is 3.0, while that of the H atom is 2.1
The result is a bond where the electron pair is displaced towards the more electronegative atom. This atom then obtains a partial-negative charge while the less electronegative atom has a partial-positive charge. This separation of charge or bond dipole can be illustrated using an arrow with the arrowhead directed toward the more electronegative atom.
$\underset{H-Cl}{\overset{\delta +\delta -}{\to }}$