You have one RLS account. This account has an accountid (prefixed with "acc") and a BTC balance. When a lightning withdrawal is sent from the account this balance decreases, and when a deposit is received this balance increases.
Every account has at least one on-chain Bitcoin deposit address (see Deposit Intents below) that allows the balance to be credited on-chain. A common workflow for organizations is to top up their RLS account on-chain when the balance is running low.
An account also has an available_balance which is the account balance minus any holds. Holds will exist on an account for any PENDING, non-settled lightning withdrawals.