Final answer:
The term that best defines vaccines used at the discretion of the veterinarian and the client is Noncore vaccine.
Step-by-step explanation:
The term that best defines vaccines used at the discretion of the veterinarian and the client is Noncore vaccine. Noncore vaccines are optional vaccines that are recommended based on individual factors such as the animal's lifestyle, travel, and exposure risks. Examples of noncore vaccines include vaccines for Lyme disease, kennel cough, and FIV (Feline Immunodeficiency Virus).