Eye of Providence

symbol of all-seeing eye (usually shown in triangle and/or surrounded by rays of glory)

The Eye of Providence, also known as the All-Seeing Eye of God is a symbol that is often used in a religious context. Very often, it is shown as a single human eye, surrounded by triangle and rays of light or glory. It is often seen as a symbol for knowledge, trinity or for a god that "sees all". The most common depiction of the Eye of Providence is in the back of the Great Seal of the United States, which is depicted on the United States one-dollar bill. In a Christian context, it is often inside a triangle, where the triangle represents the Trinity. Freemasons also use the symbol, there it stands for knowledge.

The Eye of Providence can be found on the reverse of the Great Seal of the United States, as seen on the U.S. $1 bill, depicted here.
Eye of providence, near Aaachen cathedral, in Aachen.