Several question on this issue. Many churches use this term to convict those in the pews and fill the altars. With this said .....
1) What does "bcakslidden" mean to you?
Apostasy
2) Can a born-again believer become backslidden?
No
3 Blessed be the God and Father of our Lord Jesus Christ, which according to his abundant mercy hath begotten us again unto a lively hope by the resurrection of Jesus Christ from the dead,
4 To an inheritance incorruptible, and undefiled, and that fadeth not away, reserved in heaven for you,
3) What would cause a believer to become backslidden?
nothing
37 Nay, in all these things we are more than conquerors through him that loved us.
38 For I am persuaded, that neither death, nor life, nor angels, nor principalities, nor powers, nor things present, nor things to come,
39 Nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord.
4) If a backslidder were die, or the Lord returned, while they were backslidden, would they inherit the Kingdom?
backsliders are apostates...they go to hell
4 For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost,
5 And have tasted the good word of God, and the powers of the world to come,
6 If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.
7 For the earth which drinketh in the rain that cometh oft upon it, and bringeth forth herbs meet for them by whom it is dressed, receiveth blessing from God:
8 But that which beareth thorns and briers is rejected, and is nigh unto cursing; whose end is to be burned.
9 But, beloved, we are persuaded better things of you, and things that accompany salvation, though we thus speak.
5) Is it possible for the entire congregation to become backslidden? :
13 But he answered and said, Every plant, which my heavenly Father hath not planted, shall be rooted up.
14 Let them alone: they be blind leaders of the blind. And if the blind lead the blind, both shall fall into the ditch