An action initiated while skydiving when your main chute has a malfunction, i.e., when it's fucked up and you want to be able to go skydiving again sometime as opposed to being well and thoroughly dead, which you will most certainly be if you go "splat" upon the ground. So you pull the cut-away handle on the right side of your harness and then hook your thumb through your reserve chute deployment handle, and pull that too. Then you hope really hard that your reserve chute doesn't screw up, 'cause if it did, that's all she wrote. You are quite possibly beyond all hope.