Savasana - Corpse Pose
"Sava" means "dead body" in Sanskrit. To practice this asana, one should lie motionless on the floor like as dead body in order to secure complete relaxation of all parts of his body and remove tensions, both physical and mental.
Shalabhasana - Locust Pose
"Shalabha" means "locust" in Sanskrit. The final position of this asana resembles a locust when it lowers its head to eat and raises its tail. Hence, the name.
Siddhasana - Pose of an Adept
"Siddha" means a spiritually enlightened person in Sanskrit.
Sirshasana - Head stand
"Sirsha" means "head" in Sanskrit. It is required to "stand on his head" in this asana and hence the name.