What is the meaning of detection?

noun

• The perception that something has occurred or some state exists.
  • usage: "early detection can often lead to a cure"
  • synonyms: sensing
• The act of detecting something; catching sight of something.
  • synonyms: catching, espial, spying, spotting
• The detection that a signal is being received.
  • synonyms: signal detection
• A police investigation to determine the perpetrator.
  • usage: "detection is hard on the feet"
  • synonyms: detecting, detective work, sleuthing