Blinking is the ability to think of a location and be there in the "blink of an eye". This is the power of a warlock (and some demons), as their way of Teleportation. Blinking is an instantaneous transfer, accompanied by a short, sharp sound. The Charmed Ones created a potion that would blind the warlock from blinking.
According to Melinda Warren, her lover Matthew Tate copied his power of blinking from another witch. This explains that the power to blink was originally the powers of witches, but after it was stolen by warlocks centuries ago, it started manifesting within them instead of witches, making it a warlock's power.