Each account contains a certain amount of allocated service units (SUs), or computational resources. The SUs are deposited via different types of allocations (see allocation of service units), and shared by all users of the group. When a job is finished, the actual SUs consumed by it will be subtracted from the balance of SUs in this account. Job submission will be rejected if the associated account has a negative balance.
One user can have access to multiple accounts, and therefore spend SUs from different accounts by running computational tasks. Each user has a default account to be associated with, and they can choose which account to be charged for that task in the SLURM job description. (For more information please see the Using Midway).