What is polarity?

In physics, polarity is a description of an attribute, typically a binary attribute (one with two values), or a vector (a direction). For example:

• An electric charge has a polarity of either positive or negative.
• A voltage has a polarity, in that it could be positive or negative (with respect to some other voltage, such as the one at the other end of a battery or electric circuit).
• A magnet has a polarity, in that one end is the "north" and the other is the "south".
• The spin of an entity in quantum mechanics has a polarity - positive or negative.
• Polarized light has waves which all line up in the same direction.