3a312c46_tal_Commodities___Bitcoin_Wiki__Ideal_Implementation
[Property] Offline Transactions C [Notes] Bitcoin can be used in off-line transactions using physical representations, like Casascius physical bitcoins and Bitbills, that give parties an assurance, through producing tamper evidence upon redemption, that the bitcoins they represent have not been spent. With computers but no internet access, transactions can be constructed for publication when either party gets online. [Ideal Implementation] 
ideally two participants should be able to safely transact without requiring internet access or trust of one another (like normal cash)
Ideal Properties of Digital Commodities - Bitcoin Wiki
Ideal Implementation