Puzzle of the week #268

Level: 
3-Bishop
Chess Diagram: 

rq---rk-
pb-p-ppp
-p--p---
--b-n---
--P-P---
--NB--P-
PP-Q-PP-
RN---RK-

The most dangerous weapon a player has is not his Queen, but the element of surprise! When you take the opponent by surprise, you don't need to use a very fancy or complicated piece of tactics to win. Look at our current position: black has the Queen and remaining light pieces pointing toward white's castle, as well as the pin on the f2-pawn; however this can't be enough for a quick win, can it? At least this is what white thought. Your tasks (black to move):
a) What kind of pin is this?
b) Use the pin to win the game for black

Total available points for this puzzle is 20. The answers will be published next time together with puzzle #269.

Puzzle #267 solution:
Game Blackburne - Day, Derby 1876. Thank you all who annotated the game! You all get full points for the effort. Of course each one of you had written different things, as you are differetn individuals; what matters is that you made an effort to think about it and write it down. It is the main purpose of the puzzle and you have achieved it.

Correct solutions:
Benjamin, Cody, Terry, Coco, Bradley, Deryk - 25 points

Comment: 

Absolute pins