What is a simile!

The definition of a smilie is

A figure of speech involving comparison of one thing with another thing of a different kind, used to make a description more emphatic or vivid

Ex:

Cute as a kitten

As busy as a bee

Life is a box of chocolates, you never know what your gonna get

Basically it means comparing two different things making something seem more empathetic.

It's a facial expression of happiness