Euler’s identity is an equality found in mathematics ... include Euler's Formula and Euler's Theorem, both of which can mean different things depending on the context. According to the USNA ...

Euler's identity: Math geeks extol its beauty, even finding in it hints of a myste­rious connected­ness in the universe. It's on tank tops and coffee mugs. Aliens, apparently, carve it into crop ...

When invited to elucidate its meaning, the visitor just chuckled. In fact, this equation, familiar to mathematicians and greatly admired for its elegance, is known as Euler’s Identity.