For a character who's legs are of a noticeably different species than the rest of the character. This is different than a character who has a split form, though they are not mutually exclusive. These characters are typically chimera.
The most notable difference is that for a character with animal legs, the 'division' between different species parts is partway down the leg. The groin is not included. If the character in question has a pelvis that is the same species as the legs, consider tagging split form instead.
Be aware that some fur markings or patterns can look like animal legs, so be careful!