Definition to be reviewed for generality across tetrapods. Typically we regard the caudal region as immediately following the sacral region, with the caudal (tail) region defined as post-anal.

Region of the vertebral column posterior to the sacrum consisting of two to four vertebrae. The last of these vertebrae is distinguished by the possession of a well-developed haemal arch; it supports the posterior part of the cloaca and marks the posterior limit of the trunk.[AAO]

uberon

cloacal vertebrae series

UBERON:0011271