Standard Edition (SE), Standard Edition One (SE1) and Standard Edition 2 (SE2) can be licensed on a per socket basis.
Each set of four, or less, Amazon vCPUs is counted as 1 socket.
Standard Edition (SE) can be licensed on a maximum of 16 vCPUs (4 sockets).
Standard Edition One (SE1) and Standard Edition 2 (SE2) can be licensed on a maximum of 8 vCPUs (2 sockets).
SE2 can also be licensed by Named User Plus (NUP) with a minimum of 10NUPs per 8 vCPUs.
"Count two vCPUs as equivalent to one Oracle Processor license if multi-threading of processor cores is enabled, and one vCPU as equivalent to one Oracle Processor license if multi-threading of processor cores is not enabled." (1)