It is a facial Expression used mostly by female and little kids but also men to try get what ever they want. It is done by puffin one lip over the other into a frown.
v. pout·ed, pout·ing, pouts
1. To exhibit displeasure or disappointment; sulk.
2. To protrude the lips in an expression of displeasure or sulkiness.
3. To project or protrude.
When a male or female puff their lips out & having a straight face in a way of trying to be sexy.