To ruin something is destroy it completely so that it is no longer useful. This may apply not only to the financial or emotional state of a person but also to their health or the physical state of a building, city or institution.
A ruin can therefore be the remains of a building city or state (as in Roman ruins) or the condition of having been wrecked or decayed. A politician's career may be left in ruins following the public disclosure of some unethical act.
Ruin can also refer to something that leads to the downfall of someone or something. Gin was often known as "Mother's ruin".