What is Grin?

Grin definition and meaning on Dictionary terms:
verb (used without object), grinned, grinA.ning.
to smile broadly, especially as an indication of pleasure, amusement, or the like.
to draw back the lips so as to show the teeth, as a snarling dog or a person in pain.
to show or be exposed through an opening, crevice, etc.

verb (used with object), grinned, grinA.ning.
to express or produce by grinning: The little boy grinned his approval of the gift.

a broad smile.
the act of producing a broad smile.

the act of withdrawing the lips and showing the teeth, as in anger or pain.