《汉堡规则》给提单下的定义是：Bill of lading, means a document which evidences a contract of carriage by sea and the taking over or loading of the goods by the carrier, and by which the carrier undertakes to deliver the goods against surrender of the document. A provision in the document that the goods are to be delivered to the order of the document. A provision in the document that the goods are to be delivered to the order of a named person, or to order, or to bearer, constitutes such an undertaking.
《中华人民共和国海商法》1993年7月1日施行第71条规定：“提单，是指用以证明海上货物运输合同和货物已经由承运人接收或者装船，以及承运人保证据以交付货物的单证。提单中载明的向记名人交付货物，或者按照指示人的指示交付货物，或者向提单持有人交付货物的条款，构成承运人据以交付货物的保证。”
提单的主要关系人是签订运输合同的双方：托运人和承运人。托运人即货方，承运人即船方。其他关系人有收货人和被通知人等。收货人通常是货物买卖合同中的买方，被通知人是承运人为了方便货主提货的通知对象，可能不是与货权有关的当事人。如果提单发生转让，则会出现受让人、持有人等提单关系人。
