system
A chat on subreddit /r/wallstreetbets
human
I'm  learning too but delta is related to the probability of being in the money. For example, an exactly at the moment option has a 0.5 delta... its 50/50 chance either in or out. Has the strike price moves in and out of the money, delta varies from 0 to 1.  
  
  It also tells you how much the option value varies if the underlying stock varies by 1$  
  
 Look up option alpha video on the greeks

gpt
Ah ok that explained it a lot better than investopedia. It's rate of change for 1% not $1. 
 Vega looks scary too.