Kissing refers to mouth-to-mouth contact between men, whether it stands on its own or happens alongside other activity. As a tag it points to the presence of that contact, not to how much of a scene involves it. Some viewers look for it as a sign of affection and closeness between partners rather than a specific sex act. Related vocabulary you may see around this term includes blowjob, anal, 69 and big cock, which name particular acts, and bareback, which describes sex without a condom rather than an act in itself. Kissing sits apart from these, since it describes contact between mouths and nothing further.