AssumeUTXO is a proposed mode for bootstrapping new full nodes that allows them to postpone verifying old block chain history until after the user is able to receive recent transactions.
Embedded in the code of the node would be a hash of the set of all spendable bitcoins and the conditions necessary to spend them (the UTXO set) as of a certain recent point in time. Similar to the existing assumevalid setting and other parameters used by nodes to converge on consensus, revisions of the assumeutxo hash would be checked for correctness by developers during code review. This would allow operators of new nodes to optionally trust that hash and download a UTXO set that matches that hash. For blocks produced subsequently to the UTXO set hash, the node would verify new blocks and update their own UTXO set like any other node without further trust. As currently designed, the node would also download and verify older blocks in the background so that it could eventually prove that the hash it first started with was correct.