Adjective
nondefault (not comparable)
(chiefly computing) Not default.
If you specify an Availability Zone group but don't specify an Availability Zone in the Spot Instance request, the result depends on whether you specified the EC2-Classic network, a default VPC, or a nondefault VPC. Source: Internet
Physical interfaces also are assigned to nondefault VDCs from the default VDC. Source: Internet
Note that for a nondefault VPC, you must specify the security group by ID using this parameter. Source: Internet