A cyst is a closed sac, and can look rather like a bubble in the tissue. It may contain air, fluid or semi-solid material. A collection of pus is an abscess, not a cyst. The kind of cyst we're interested in here is a stage in the life cycle of a parasite.
Lesions, by contrast, are abnormal changes in animal tissue (meat, organs and other body parts), according to ‘Parasitic cysts and lesions in organs’, a leafet produced by the Department of Agriculture, Land Reform and Rural Development
