This is money that is being kept in a separate bank account. It is often a component of Restricted Assets which may include investments that forms part of a large endowment. This can also be money that has been set aside for a specific purpose and can only be used for that reason.
Funds placed in a second account from your primary one, which is restricted for specific uses such as emergencies or travel funds. So basically Restricted cash is cash reserved for a specific application or purchase.
Much like collateral, restricted cash is cash deposited in a separate account and used for a cushion against possible loss or debt. It can also be used for emergency purposes.
