Now THIS I really don't understand!
I was always taught that the shedding of innocent blood was murder (ie: premeditated murder.) Killing in self-defense or during war would not be shedding of innocent blood. Abortion doesn't fall under this, althought the LDS Church does denounce abortion as an extremely grave sin. There are various theories floating around out there that shedding of innocent blood can be denying the Holy Ghost, which is having the knowledge and then turning against it, but I've also been taught that that knowledge is actually having seen God the Father and Jesus Christ, turning against that knowledge and actually persuading people to turn against Christ.
I know in my Internet search, sites came up that talked about blood atonement (which we don't believe in) and in the fact that we allegedly don't believe that when Christ shed his blood on the cross that it paid for our sins (we do believe that shedding His blood is the Atonment and did atone for our sins. However we also must repent of those sins, or suffer in the hereafter for those sins, and then receive our degree of glory...)
So it's not exactly written in stone just WHAT it means.