What is the meaning of alertness?

noun

• The process of paying close and continuous attention.
  • usage: "wakefulness, watchfulness, and bellicosity make a good hunter"; "vigilance is especially susceptible to fatigue"
  • synonyms: watchfulness, wakefulness, vigilance
• A state of readiness to respond.
  • usage: "alerting was indicated by the desynchronization of the EEG"
  • synonyms: alerting
• Lively attentiveness.
  • synonyms: sharp-sightedness, on the qui vive