Spirits are unaging (though not unkillable), typically intangible beings who nevertheless still have a quasi-physical appearance, which they implement to interact with other beings in their world. Spirits come in many different forms, though they all have some form of control over magic. Natural spirits are usually tied to a certain place, element, and the like, and thus have magical capabilities related to such ties. Occasionally, spirits can come into contact with other beings and take on a more tangible form; some of these forms of contact result in offspring. In other cases, spirits become trapped in various objects for one reason or another, including other beings, living or otherwise. These spirits, while not as powerful as their untrapped counterparts, can still excercise some control over their powers.
Part-spirits are any being who can claim that any part of their heritage can trace back to another pure spirit. Though these beings typically cannot become intangible, they still possess power and control over their respective heritage's magic. Typically, their powers awaken at a young age, which is also when they start to age slower than others in their non-spirit race. Part-spirits must also learn how to control their powers lest they become overwhelmed and risk death, which is why most part-spirits don't make it past their first ten years. In addition, because they don't have an intangible form, part-spirits cannot possess other beings or objects nor can they be trapped like pure spirits, though they can be trapped by other methods.
Though their full potential are usually locked away in some form, many trapped spirits still maintain a form of control over their powers, be it discharging magic on contact or providing their powers to a second party or something else along those lines. Not all spirits are trapped in the same way, however; some choose to be "trapped", or rather, possess another being's body or another object for whatever reason. Others are trapped due to being tricked, outsmarted, overpowered, etc. Either way, these spirits are not at their full power and thus are not as so-called dangerous as untrapped, pure spirits.