What is the meaning of flats?

noun

• A level tract of land.
  • usage: "the salt flats of Utah"
  • synonyms: flat
• A shallow box in which seedlings are started.
  • synonyms: flat
• A musical notation indicating one half step lower than the note named.
  • synonyms: flat
• Freight car without permanent sides or roof.
  • synonyms: flatcar, flatbed, flat
• A deflated pneumatic tire.
  • synonyms: flat, flat tire
• Scenery consisting of a wooden frame covered with painted canvas; part of a stage setting.
  • synonyms: flat
• A suite of rooms usually on one floor of an apartment house.
  • synonyms: apartment, flat
• Footwear (shoes or slippers) with no heel (or a very low heel. ).