Let's talk about Layer 2 networks.
Layer 2 is a scaling network built on top of the Ethereum mainnet. Transactions are executed on Layer 2, and the results are then written back to the mainnet.
One thing that's easy to overlook: Layer 2 security relies mainly on the Ethereum mainnet. Data and proofs ultimately need to be posted to the mainnet—that's the main difference between Layer 2 and sidechains.
When making a transfer, check which network you're using: assets at the same address are separate on different networks.
$ARB is the governance token of the Layer 2 network Arbitrum.