"Post-op tranny" is a term used in adult content to describe a specific type of transgender adult film or scene. The term "tranny" is a slang abbreviation for "transsexual," and "post-op" refers to the fact that the performer has undergone gender reassignment surgery, specifically genital reconstruction surgery.
This means that in these videos, the transgender performers have already had their surgeries, which typically includes breast augmentation for female-to-male performers and genital reconstruction surgery for male-to-female performers. The content may include various sexual acts involving these performers, depending on the preferences and limits of each individual involved.
In summary, "post-op tranny" refers to adult content featuring transgender performers who have already undergone gender reassignment surgeries.