The Eye of Horus is sometimes referred to as the wedjat, and represents Horus, the Egyptian falcon-headed god. The Eye was used as a symbol of both protection and healing. When appearing as the udjat, it represents the right eye of Ra, the sun god. The same image in reverse represents the left eye of Thoth, the god of magic and wisdom.
The symbolism of eyes appears in many different cultures and civilizations -- it's no surprise that the image of an "all-seeing eye" is common in today's society! In Reiki, the eye is often associated with knowledge and enlightenment -- the Third Eye -- and it typically is connected to the true soul.
The eye symbol was painted on the boats of Egyptian fishermen before they set out to cast their nets along the Nile River. This protected the boat from evil curses, and its occupants from those who might wish them harm. The Egyptians also marked this symbol on coffins, so that the person held within would be protected in the afterlife. In the Book of the Dead, the dead are led into the afterlife by Osiris, who offers the deceased soul nourishment from the Eye of Ra.
Learn about other gods and goddesses of the Egyptians: Deities of Ancient Egypt.
The notion of the "evil eye" is a universal one. Ancient Babylonian texts make reference to this, and indicate that even 5,000 years ago, people were trying to protect themselves from the malevolent thoughts of others. Use this symbol as one of protection against someone who might harm you or your loved ones. Invoke it around your property, or wear it on a talisman or amulet as a protective device.