This porn video tag can be broken down into four parts:
1. Big tit - The performer has large breasts.
2. Tranny - The performer is a transgender woman or individual with male genitals and female secondary sex characteristics.
3. Anal - Anal penetration, or penetration of the anus, is taking place in the scene.
In summary, this tag describes a porn video featuring a transgender woman with large breasts performing anal intercourse.