A escrow account is the name for an account that is held in trust by a third party (e.g. lawyer, notary) on behalf of another person. The trustee manages the funds only in the sense of the client.
With Marvest, your investment initially lands in a trust account and is later transferred to the shipowner in bundled form. This has the advantage that the shipowner only receives one payment on his account and only posts a liability amount.