This is clearly defined in the CDISC SDTM controlled terminology (READ IT!): CDISC Terminology | CBIIT
ACTSUB definition: “Actual number of subjects enrolled; may include subjects who were not randomized”.
In your applications, you can also use the RESTful web services to find out: see XML4Pharma Web Services
For example, your application may use the following RESTful request: http://www.xml4pharmaserver.com:8080/CDISCCTService/rest/CDISCDefinitionFromCDISCTestCode/ACTSUB/TSPARMCD