ETH to ETH2 Is it a conversion or just a deposit?

Does depositing ETH to the ETH2 Deposit Contract look like a separate ETH2 is created? Or is it just a one-way deposit?

Asking this question because its often referred to "converting" ETH to ETH2 (coinbase uses this).

Looking at the ETH2 deposit contract it looks like its ETH just locked up.

When I read more about the "docking" also, it looks like the Mainnet will become a shard on ETH2.0, so once withdrawals are allowed, the same ETH can theoretically be withdrawn onto the same network?

Do I understand this correctly?