An imp is a particularly mischievous mythological being similar to a fairy or a lesser demon, frequently described in folklore and superstition. They are not strictly evil and are more mischievous than evil or harmful.
Imps are often described as mischievous more than seriously threatening, and as lesser beings rather than more important supernatural beings. The attendants of the devil are sometimes described as imps. They are usually described as lively and having small stature.
Imps are often shown as small and not very attractive creatures. Their behavior is described as being wild and uncontrollable, much the same as fairies, and in some cultures they were considered the same beings, both sharing the same sense of free spirit and enjoyment of all things they consider as fun and others may consider as mischievous pranks.
It came to be believed that imps were the familiar spirit servants of witches and warlocks, where the little beings served as spies and informants due to their abilities and wit.
"Origin: Western Europe. Familiars of witches. As long as they are magically bound, they perform simple tasks for their masters. But they scheme to betray their masters at the first possible opportunity."
—Shin Megami Tensei A-Mode DDS dictionary
DemiKids Light & Dark
"A child-demon who serves a witch. Enjoys playing tricks on humans to pass the time."