What is the meaning of coincidence?

noun

• An event that might have been arranged although it was really accidental.
  • synonyms: happenstance
• The quality of occupying the same position or area in space.
  • usage: "he waited for the coincidence of the target and the cross hairs"
• The temporal property of two things happening at the same time.
  • usage: "the interval determining the coincidence gate is adjustable"
  • synonyms: concurrence, conjunction, co-occurrence