A woman's mouth is generally shown as a pair of lips and the upper row of teeth, rather than the inside of the mouth. Its meaning can be divided into two main categories. The first category is related to kissing. In this meaning, the emoji is always followed by other emoji related to romance.
And the second, more common, is related to the process of speaking or talking or singing. In this sense, it can be used as an illustration of someone's speech or statement.
Mouth was approved as part of Unicode 6.0 in 2010 and added to Emoji 1.0 in 2015.
U+1F444
? Mouth