I will define backsliding to be turning away from God, or turning back from God. It also means to be stubborn and rebellious. When those who have been saved and born again depart from Christ in to ungodliness, then they are backsliders. Backsliding has to do with someone who has actually known God, not just church goer.
Someone that knows difference between sin and righteousness and has lived right before, to suddenly turn back to the evil he once repented from is backsliding. Some are not yet backslided, but bent to going back.
"If they have escaped the corruption of the world by knowing our Lord and Savior Jesus Christ and are again entangled in it and are overcome, they are worse off at the end than they were at the beginning. It would have been better for them not to have known the way of righteousness, than to have known it and then to turn their backs on the sacred command that was passed on to them. Of them the proverbs are true: “A dog returns to its vomit,” and, “A sow that is washed returns to her wallowing in the mud.”_ - 2 Peter 2:20-22.
When one departs from truth in to error, the goodness of God will depart from that person the previous blessings will be reversed.
The second form of backsliding is not necessarily going in to sin, but sliding back from previous known truth or standard of righteousness. A mixing up or perversion of known truth is backsliding. Stepping back from previous attainment is backsliding.
"But my righteous one will live by faith. And I take no pleasure in the one who shrinks back.” But we do not belong to those who shrink back and are destroyed, but to those who have faith and are saved." - Hebrews 10:38-39.