MSB registration is the requirement for a money services business in the United States to register with the Financial Crimes Enforcement Network, and the process is explained in full under FinCEN registration. People say "MSB registration" when they are thinking of who must register, and "FinCEN registration" when they are thinking of the agency and the filing itself; both refer to the same obligation.
Under the Bank Secrecy Act rules, most businesses that fall within the definition of a money services business, such as money transmitters, currency dealers and exchangers, and cheque cashers above set thresholds, must register within 180 days of starting business and renew every two years. Agents of a registered MSB do not register separately, but the principal must keep a list of them.
Registration is often misunderstood as a licence. It is not: it records the business with the federal government and brings it under anti-money laundering obligations, but it does not authorise any activity. Money transmitters still need a money transmitter licence in each state where one is required, typically applied for through the NMLS.