1. Based on the principle of having only one member (as of a legislature) selected from each electoral district
   - uninominal system, uninominal voting system, single-member system, scrutin uninominal voting system

Type of: electoral system, voting system

• family Sirenidae
• family Sisyridae
• family Sittidae
• family Solanaceae
• family Soleidae
• family Solenidae
• family Soricidae
• family Spalacidae
• family Sparganiaceae
• family Sparidae
• family Sphaeriaceae
• family Sphaerobolaceae
• family Sphaerocarpaceae
• family Sphecidae
• family Spheniscidae
• family Sphingidae
• family Sphyraenidae
• family Sphyrnidae
• family Spirillaceae
• family Spirochaetaceae
• family Spirulidae
• family Squalidae
• family Squatinidae
• family Squillidae
• family Staphylaceae