What it means

1. verb start running, functioning, or operating
   “the lights went on”
2. verb continue talking
   “`I know it's hard', he continued, `but there is no choice'”
3. verb continue a certain state, condition, or activity
   “Keep on working!”
4. verb come to pass
   “What is happening?”
5. verb move forward, also in the metaphorical sense
   “Time marches on”