Q: Did all mankind fall in Adam’s first transgression?
A: The covenant being made with Adam, not only for himself, but for his posterity; all mankind, descending from him by ordinary generation, sinned in him, and fell with him, in his first transgression.

Q: Into what estate did the fall bring mankind?
A: The fall brought mankind into an estate of sin and misery.

Q: Wherein consists the sinfulness of that estate whereinto man fell?
A: The sinfulness of that estate whereinto man fell, consists in the guilt of Adam’s first sin, the want of original righteousness, and the corruption of his whole nature, which is commonly called Original Sin; together with all actual transgressions which proceed from it.

(Questions XVI, XVII and XVIII from the Westminster Shorter Catechism)