Evil, in many cultures, is a broad term used to describe what are seen as subjectively harmful deeds that are labeled as such to steer moral support. Evil is usually contrasted with good, which describes acts that are subjectively beneficial to the observer. In some religions, evil is an active force, often personified as an entity such as Satan or Ahriman.
Incarnate which literally means embodied in flesh or taking on flesh, refers to the conception and birth of a sentient creature (generally a human) who is the material manifestation of an entity, god or force whose original nature is immaterial.
So, evil incarnate would be anything that would be deemed as evil embodied in flesh or taking on flesh, or alive.