What are MVNO and MVO?

MVNO - mobile virtual network operator

MNO - mobile network operation

The MNO is the infrastructure operator (provides the backbone of the mobile network), and the MVNO leases the network instead of building its own. Giffgaff (on o2), Tesco Mobile (on o2) and Lycamobile (on multiple networks) are MVNO - savvy resellers, if you will.