Aesthetics is a branch of philosophy that describes and analyzes the nature of beauty (or its counterpart, ugliness).
For an audience, beauty is that which gives us pleasure (or, ugliness > pain). So sometimes aesthetics involves the quality of the work, but sometimes it means the effect on an audience.
In this respect, aesthetics can mean "appeal." Why or how are people pleased by an artifact or product?
Besides philosophy, another place you may hear the word "aesthetics" these days is on cable TV "design shows" like Designed to Sell, Curb Appeal, or Spice Up My Kitchen. An interior designer might say, "This room is comfortable, but we need to improve its aesthetics"--that is, "make it look better," more beautiful or pleasing.
Another recent use is "Aestheticians" (facial & body enhancements--see website)