The "nerdy-girl" tag in a porn video refers to a female performer who is portrayed as having a nerdy or geeky appearance and personality. This could include characteristics such as wearing glasses, displaying intellectual interests, dressing in a more reserved or academic style, or engaging in activities like reading, gaming, or studying.
In adult content, this theme can be used to present a contrast between the performer's nerdy exterior and their passionate, sexual side. It can also cater to individuals with a specific preference for women who possess these qualities, both physically and in terms of personality traits.