Monzo offer "pots" - a space to hold money, that operates similarly to a savings account. For more info on pots - see this guide from Monzo: Understanding Pots
Depending on your use case - you may wish to filter our transactions into, or out of, pots. You can use the provider_category value in the meta field of the /transactions response to do this.
Monzo pots transfers, for retail bank accounts, are returned with the provider_category of uk_retail_pot. (Please note that alternate values may be returned for non-retail Monzo accounts)
Please note: The meta object in the /transactions response is a collection of additional provider specific transaction metadata - it may not always be returned by the provider.