What is the hinder part of any covering for the foot, as of a shoe, sock, etc.; specif., a solid part projecting downward from the hinder part of the sole of a boot or shoe called?

heel — The hinder part of any covering for the foot, as of a shoe, sock, etc.; specif., a solid part projecting downward from the hinder part of the sole of a boot or shoe. (Webster's 1913.)