In the context of a porn video tag, "fat shemale (shemale)" refers to a performer who identifies as a shemale. Shemales are individuals who have both male and female characteristics in terms of physical appearance or sexual identity. In this particular case, the term "fat" is used to describe their body type or physique.
Shemale is often considered as an umbrella term that can include various gender identities such as transgender, transsexual, or non-binary individuals who have developed male-typical secondary sexual characteristics like facial hair and/or a larger frame due to hormone therapy or natural hormonal changes. It's essential to understand that these tags are for adult audiences only and should be approached with sensitivity and respect towards the performer's identity and expression.