The porn video tag "iknowthatgirl" refers to a scene or content involving recognizable adult film actresses. This phrase is commonly used by fans who are familiar with specific performers and want to search for videos featuring those particular stars. In this context, "I know that girl" means that the viewer is aware of the actress's work and wants more content with her involvement. It can also imply a sense of excitement or familiarity towards the actress, as fans often have favorite performers they enjoy watching in various scenes.
For example: In a video tagged "iknowthatgirl," the viewer might recognize the female lead from previous films and be excited to see her featured again, potentially in new and exciting situations. This tag is used to identify content that includes known actresses for those who have followed their work or are fans of their performances.