http://en.wikipedia.org/wiki/Clawback http://www.investopedia.com/terms/c/clawback.asp http://pandodaily.com/2012/04/26/founders-should-give-their-stock-back-why-vesting-is-in-your-startups-best-interest/ The two are not related - but conditions on issuing shares can have clawback provisions. For example: Zynga has contractual provisions that states the company gets back shares (clawback) from founders under certain conditions (possible ones: leave too early, terminated under bad circumstances, miss objectives, etc).
So, they're similar in that they're both ways to take back shares that have already been awarded.
With "Vesting," the idea is that as you perform services, you "earn" the right to keep shares or options that have been awarded to you. The longer you work for the issuer, the more shares you get to keep. If you leave, then any "unvested" shares/options usually revert to the issuer.
A "Claw-back" is where shares are awarded, but can then be taken away based on some contingency -- not making a revenue target or missing a milestone, for example.