Evil is a concept that varies greatly according to tradition. Generally, it is a force of destruction or disruption.
Many religions have a creator God or tutelary deity that symbolizes goodness, rightness, or morality or who has put forth rules to live by. It may be found, not just as actions that are harmful to others, but in actions, and even attitudes that counter the established morality of the community, even if they cause no real disruption or harm to anyone else. Evil then would be represented by actions that counter the Will or instructions of this God and may be personified in a God or various spirit beings at odds with the “good” God(s). Here, evil may be represented not just in the actions of people, but also in natural processes, disasters, disease, and death.
In this case, evil may something that tempts one to stray from the defined path or accepted norms of behavior. Evil then comes from without rather than within and may be something that the evil-doer must fight and may expect help from the community to do so. However, succumbing to evil may be seen as such a personal and moral failure that the evil-doer must be driven out or destroyed to prevent the evil spreading to other people, or to other areas of the environment. If evil is a violation of the Will of God, then, of course, evil behavior can cause God to withdraw His blessings and “goodness” causing additional evil to befall; such as natural disasters, crop failures, diseases, etc.
In the absence of a Divine Will, the idea of evil may be present in anti-social behavior that severely disrupts the normal functioning of a group. Evil here is found within the individual, based on personal acts and Wills of the evil-doers themselves. It is intentional disruption or destruction and might be brought about by emotions, such as spite or jealousy or by something innate within the evil-doer. It is necessary to remove the evil-doer from the community not to prevent the contagion of evil or the withdrawal of blessings, but to protect the rest of the community from being harmed by the future actions of the evil-doer.
When we speak of evil in modern magical vernacular, we are generally talking about disruptive forces that can bring harm without regard to a defined morality and we may be referring to human individuals who enter a situation with malicious intent, we may be referencing a spirit being, or, occasionally, a miasma of residual energy that causes a the sort of negative feelings that might inspire disruptive behavior (jealousy, discontent). When we are banishing evil, or shielding ourselves or space from evil, we are generally trying to clear the air of unpleasant feelings and protect ourselves from anyone who might wish us harm, whether they be corporeal or incorporeal beings.
Many witches today avoid using the term “evil” because in a culture steeped in Abrahamic attitudes, the idea of evil implies a dichotomy of evil and good that witches tend to reject in recognition of the necessity of the natural forces of creation and destruction and the belief that these exist without morality or judgment, but rather depend on necessity. Evil is recognized as an objective term with imprecise meaning clouded with prejudicial overtones. Thus, rather than banishing or warding against evil, a witch may prefer to banish or ward against “those who would do us harm” or “any who do not have our best interests at heart” or “any energy contrary to our purpose” as this provides more precision in meaning.