Head Canon

Headcanon (often misspelled Headcannon) refers to the personal way a person views the fluffyverse. For example, person A may say, "In my headcanon, mares do not fluffsplode, and fluffies are mostly Feral," while person B may respond, "In my headcanon, mares always fluffsplode, and fluffies are mainly domesticated." While headcanon preferences vary from person to person, most stories and pictures follow a generally accepted canon, often called the "hivecanon" or the "community headcanon".

General Canon
There are many more examples, but the list would be enormous. It is worth noting that most people accept somebody's headcanon without argument, so it isn't necessary to change things that aren't the norm.
 * Fluffies are accident-prone, and unintelligent.
 * Fluffies crave spaghetti.
 * Fluffies love foals, and reproduce rapidly.
 * Fluffies, unless mentally defunct, love hugs and love
 * Fluffies communicate via a babytalk.
 * Fluffies are hardwired to trust humans.
 * Fluffies are generally weak

Worth noting is that typically fluffverse terminology will have the same meaning from headcanon to headcanon, such as "Smarty Friend" or "Sorry Stick", unless defined otherwise.