Backsliding is when a believer turns back to sin or becomes stubborn in their heart to the will of God in their lives.
Backsliding starts in the heart and then finds expression through outward action. The outward actions are only symptoms of the real problem.
The attitude of the heart must be dealt with in order to change the actions.
Backsliding is closely aligned with carnality in that one's own desires and devices are acted out as opposed to God's will.