This describes a moment before a kiss occurs between characters. A character's mouth must be in close proximity to another character's for the purposes of this tag. Often there will be head tilting, blushing, chin grabbing, eye closing (alternatively, direct eye-to-eye contact) and other such bodily cues present on the subjects in question.
Not to be confused with incoming kiss, which is an incoming kiss from a single character in the picture towards the viewer.
Depending on how ambiguous it is, this tag may overlap with after kiss.