The porn video tag "cum-in-her-mouth" refers to a specific sexual act depicted in the video. In this scenario, a male performer ejaculates (cums) into the mouth of a female performer. It implies that the male character reaches orgasm and releases his semen into the oral cavity of the female character, who may or may not swallow it. This type of scene can be found in many adult films and is often used as a climactic moment in the video.