CREATE TABLE table_18081 ("Complete Series" TEXT, "Region 1" TEXT, "Region 2" TEXT, "Region 4" TEXT, "DVD Extras and Bonus Features" TEXT, "Number Of Discs" FLOAT)

Name the region 4 for the complete fifth series
SELECT "Region 4" FROM table_18081 WHERE "Complete Series" = 'The Complete Fifth Series'
SELECT "Region 4" FROM "table_18081" WHERE "Complete Series" = 'The Complete Fifth Series'