today i review my Search Analytics in google webmaster console
i see some keyword has negative Position number
what does it mean??
Google Webmaster Console average position is reportedly buggy but in your case, it's a difference between last month avg position and this month avg position.
In July/August you had ranking position 130 and in Aug/Sep your ranking position was nill, Google considered it as zero so as per calculations you lost 130 positions and difference is -130.
Let me know if anything is still unclear!