difference between pre-mining and mining I am new in blockchain and not an IT person.

is there a difference between pre-mining a cryptocurrency and mining a block? 
I do understand the rewarding action when a miner solves a hash puzzle to add a block to the chain.  However, I do not get the pre-mining activity.  Maybe I am mixing up 2 different functionalities.
Pre-mining means that new coins have been mined before the coin has been made public. Which means the creator of the new currency had an unfair advantage and started with a large amount of coins before anyone else had the chance.
Pre-mining often deters other people from joining and any currency is useless without users.