"Infusion" in the context of a porn video tag is likely referring to a scene or act involving the injection or insertion of a fluid, typically semen, into one or more parts of the body. This could be an injection into the scrotum, the urethra, the anus, etc., or it may involve a character receiving fluids through various orifices, such as through the mouth or an open wound. The tag suggests a scene involving fluid exchange or manipulation in a sexual context.