I've thought up this story for a while and I just started writing off a whim. Anyways, onto the basic info:

Familiars
Familiars are spiritual beings attached to wizards regardless of blood status or talent. They don't often show themselves to the people they are tethered to unless they feel the need to. Familiars are closely connected and can greatly influence the patronous a wizard has.

Bonding
Bonding is when the Familiar and it's handler have become so attached to each other that they form a special connection with each other or "bond." The bond is symbolised by the gifting of an item to the handler from the familiar; often a piece of jewellery of some sorts. If the bond is broken, the familiar no longer becomes attached to its handler and they are free to roam as they please. However, if the bond wasn't mutually decided upon the familiar will start to suffer, and in extreme cases: die. It should be noted that a familiar can bond with someone other than their handler, but it wouldn't be nearly as strong.

Traits/Abilities
Familiars are often animalistic in there true form, but they are essentially humans. The animal attributes are often similar to the patronous of the wizard or of any animals closely associated with their handler. Familiars are taught magic like wizards and use a wand, but they are adapt at using wandless and non-verbal spells. Familiars have the ability to shift between forms (true and human) as well as possession, levitation, and any helpful skills they carry over from their true form.

It should be noted that familiars are essentially human beings with their own thoughts and emotions, but they are attached to someone else and can be degraded like a peasant class.