selective service
noun [ U ] US uk/sɪˌlek.tɪv ˈsɜː.vɪs/ us/səˈlek.t̬ɪv ˈsɝː.vɪs/
（美国的）选征兵役制，义务兵役制
the system in the US in which men aged 18-26 must put their names on an official list so that they can be called to join the army if there is a war
Compare: national service