Endothermy (or warm-blooded) means that a stable body temperature despite heating or cooling of the environment must be maintained (requires a lot of energy to have an endothermic system).
Ectothermy is when body temperatures of the organism vary with external conditions because the body has not developed a system to keep the internal heat constant. When talking about whether Velociraptor was endothermic or ectothermic there are a number of points to be considered.

Upright Posture Predator-Prey Ratio
Large Brain Bone Evidence
Widespread Ranges Bird Link