The survey population is the set of elements identified by the frame. For instance, pre-election polls have "likely voters" as a target population, but the survey is conducted using RDD (usually). The survey population is households with active land-line telephones, because that's who we can initially identify. Survey questions help narrow the respondents into the desired set, but then eliminating sampled units increases variance. It is reusable in the sense that the same survey population will be used each time the named frame is used.