'Weak' in the Bible

but the foolish things of the world did God choose, that the wise He may put to shame; and the weak things of the world did God choose that He may put to shame the strong;

but not in all men is the knowledge, and certain with conscience of the idol, till now, as a thing sacrificed to an idol do eat it, and their conscience, being weak, is defiled.

and thus sinning in regard to the brethren, and smiting their weak conscience -- in regard to Christ ye sin;

Because of this, among you many are weak and sickly, and sleep do many;