There are many potential causes of vomiting in cats, but yellow liquid specifically can indicate a few different things. If your cat is otherwise healthy and has no other symptoms, it's likely that they simply ate something that didn't agree with them and their stomach is trying to get rid of it. However, if your cat is vomiting frequently or has other symptoms like lethargy or appetite loss, it could be a sign of a more serious underlying condition such as liver disease or an intestinal blockage. If your cat is vomiting yellow liquid regularly or showing other concerning symptoms, it's best to take them to the vet for an evaluation.