The Medical Subject Headings list in PubMed defines bioethics as "a branch of applied ethics that studies the value implications of practices and developments in life sciences, medicine, and health care."
Britannica defines bioethics as a "branch of applied ethics that studies the philosophical, social, and legal issues arising in medicine and the life sciences. It is chiefly concerned with human life and well-being, though it sometimes also treats ethical questions relating to the nonhuman biological environment. (Such questions are studied primarily in the independent fields of environmental ethics and animal rights.)"
For a longer reflection on the nature of bioethics, visit the "What is Bioethics?" page at the Center for Bioethics and Social Justice at Michigan State University.