Please note when I talk about subs I may use the pronoun she but I am aware that people of all genders can be subs. I had to look up these meanings to make sure I was getting these right and then I realized there are so many. I had no clue that there were so many. I know about day collars and protection collars but there are so many styles and types.
One of the most well-known is the basic, or standard, collar. These are the ones you see around BDSM, like protection, consideration, training, and formal or permanent. This may also include day collars.
Some doms opt for branding, piercings, or tattoos because they go on the skin and can be permanent. With branding, it can be a tattoo or actual branding, like cattle of some sort. This is to be done when you know that you are going to be with this person forever because you really wouldn't want to have a brand or tattoo after a break up. Piercing is another option that's less permanent. They're usually on places like nipples, the clit, or the penis. Sometimes, the piercing may have a chain on it, commonly on the nipples. With tattoos, it maybe a name, Barcode, band around the arm, collar around the neck, or anything.
There are also dress collars for special occasions and sophisticated outings. It's usually metal, sometimes engraved or with stones on it. It doesn't really look like a collar because it doesn't have BDSM hardware on it.
There are house collars, too. These are used in a house, a dungeon, or at a club, party, or at events. They are usually made of leather with a lock or some way of securing it, usually on the back. Most of the time, the collars will have a piece of "hardware" that can be hooked up to a restraint or a lead or leash. There is also a posture collar that holds your head at a certain angle or higher. They are usually used instead of a house collar in a session. Play or scene collars are also used in scenes or sessions. It's used for a short period of time but it could be used to show ownership at clubs, events, or parties. The play collar is a great way to get a sub into the mindset of a sub.
There's also the protection collar which, as the name suggests, the sub wearing it is being protected by a dom. The protection collar is worn by the sub until she or he is ready for a relationship. Once the sub is in a relationship, the dom can still protect or mentor her. The sub can wear a protection collar for many reasons like abuse, not being ready for a relationship, or the sub is being trained. There are so many reasons why these are used.
If a sub is not ready for a relationship or fresh out of one but no one will put a protection collar on them, they can self-collar. They are telling the world to back off and give them time to heal.
Public collars are widely used and known in the lifestyle, sometimes called day collars. It is used for those moments when the couple interacts with vanillas or go out somewhere. These can be anything from a choker, to a necklace, to a chain with a lock acting as a charm.
A trial collar, or collar of consideration, is one worn by a sub when the relationship is new and you want to make sure that you want to be with this person. Once you are sure, there is a training collar for when you are training your sub. If a training collar isn't needed, there's a permanent collar. It's kind of the BDSM version of being married.