New to Custom Tokens

Much recently, when I first installed and start using Hive Keychain, I could have seen the few custom token in my account.

Frankly speaking, I have no clue about custom tokens and how it appeared in my account. Among few, it includes the Leo token and similar others.

Now, in this post my interest is to get an idea generally about custom tokens and the way to manage it.

1. What are these custom tokens
2. Are these token tradable?
3. If yes Where?
4. And anything relevant

Thanks