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 multithreading 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)
"Oracle Database@Azure is an Oracle database service running on Oracle Cloud Infrastructure (OCI), colocated in Microsoft data centers" (2)
"Oracle Database@Azure runs on infrastructure managed by Oracle's expert Cloud Infrastructure operations team. The operations team performs software patching, infrastructure updates, and other operations through a connection to OCI. While the service requires that customers have an OCI tenancy, most service activities take place in the Azure environment." (2)