what is the main difference between etherbase and coinbase? And what is the meaning of "uncle" in a transaction?
Coinbase and Etherbase are the same, which is your default address where mining reward is going/credited in.
Uncle is a block that in bitcoin would be considered an orphan because its not on the longest chain (it's an alternative block at the same height as your parent). In some content I heard people refer it as family tree Dad and you are correct chain where uncle is almost correct but not accepted one.