PLEASE EXPLAIN ‘PREMINED’

Okay, so I'm really new to the crypto world, and the only thing that peeked my interest aside from BTC is investing in the Ethereum platform.

Now, BTC wasn't PREMINED meaning that Satoshi actually started mining the coins well after he announced the coin.

I assume Ether is PREMINED using the Ethereum platform, right?

Does that mean?

1. The founders first mined the coins and than after the fact announced the existence of a platform/coin?

2. They awarded the Ether coins to themselves in some other way?

Please ELI5 the concept of 'premined' when it comes to Ethereum or Ether ( I still don't understand it fully).

Thank you so much.