Glossary Please select an letter from the A-Z list or search # A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ulcer A break in the skin or mucous membrane which involves the loss of the surface tissue. undetectable viral load A level of viral load that is too low to be picked up by the particular viral load test being used. uveitis Inflammation of the middle layer of the eye.