It should be quite obvious if you just check your point history, but OK, here:
Let's say you have 41 points. Precious, shiny, totally not pointless points that you worked oh so very hard for.
Then you do something stupid, as is the wont of noobs. Bad boy! An admin decides to give you a penalty, a punishment for your misbehavior (spamming, in this case).
So they dock/remove/subtract/deduct/take away 10 of your points, with the reason "Spam comments". You now have 41 -10 points. That's 31 points.
For more information, you can check the dictionary; dictionaries are wonderful! For example, you can read the second definition for the verb dock on dictionary.com.