From Sajun.org

A bubble may take the form of:

  • a pocket of air or gas caught within a solid or liquid
  • a spherical liquid film (often of surfactant, occasionally of bubble gum) filled with air or gas
  • a metaphor for isolation (e.g. 'living in a bubble')
  • a (normally) transparent dome

See also: soap bubble, bubble (economics), antibubble, Westminster Bubble