"Gay Grandpa" is a porn video tag indicating a specific type of adult content. In this case, the tag refers to scenes involving a grandpa character who engages in homosexual activities or has sexual relations with other men, usually younger ones. This is targeted towards an audience that is into gay senior themed content. The word "gay" further specifies that the content involves male-male sexual activity. It's essential to note that this tag is only for adult audiences familiar with porn videos and their explicit nature.