"Fearful behavior" refers to actions that someone does when they are feeling scared, anxious, or intimidated. It is their way of responding to their fears or concerns. Full definition
Many people don't understand the importance of socialization at this early age as it applies to prevention of aggression and fearful behavior in the future. (acanineaffinity.com)
For dogs that are in the early stages of training and still showing a lot of fearful behavior, that is the place they need to be for theirs and others safety. (austindog.org)
Simply ensure that you don't reward fearful behavior with more attention. (thesprucepets.com)